Chapter 1: 13 Reasons Why
"Whether it's the City of Gold or Sky Island, there's never been a person who's proven they don't exist!"
-Montblanc Cricket
-Montblanc Cricket
Foreword: This theory ended up being a lot longer than I originally intended it to be, a little over 50,000 words in fact. To put that into perspective, that's generally considered to be novel length. There are enough topics covered here that I could have made at least ten different theories, and while I may have gone into a bit more detail on them here than maybe was necessary, I do feel that including those theories here contributes to the overall strength of this theory, as not only does it not require one to jump back and forth between outside readings to understand the content of this one, they also serve one of the greater themes behind this theory: the connection of loose threads. Given that no character or event in One Piece exists in isolation, I feel that discussing only one is near impossible without connecting it to other characters or events. That said, because of how much information I ended up cramming into this one theory, it ended up taking me nearly a month to write, and may be somewhat difficult to read through. I have divided this theory into its relevant chunks and provided summaries where appropriate. Please do not feel obligated to read everything at once, and feel free to read the summaries if you just want to see the conclusions with a small bit of the evidence. Do note though that the majority of the evidence, as well as alternatives and counterarguments that I suggest or eliminate, will only be in the main body and not the summaries. Take your time, be respectful, and above all, please enjoy yourself.
- Chapter 1: 13 Reasons Why (The Evidence)
- 1.01: Monet’s Heart is Shown Intact
- 1.02: Monet’s Backstory and Relationships
- 1.03: Monet’s Interest in Astronomy
- 1.04: Monet’s Tattoo
- 1.05: Monet’s Wings (and Other Bird Parts)
- 1.06: The Shinokuni Search Team
- 1.07: Monet’s Personality
- 1.08: Luffy’s Love of Snow
- 1.09: The Sea Rabbits
- 1.10: The Note Thrown to Chopper
- 1.11: Big Mom’s Collection
- 1.12: The Snowman Color Spread
- 1.13: Miscellaneous Patterns
- 1.14: Chapter 1 Summary
- Chapter 2: The Vegapunk Saga (Monet's Return)
- 2.01: Filling in the Blanks (Where She’s Been)
- 2.02: Monet the Straw Hat (Monet’s Role)
- 2.03: The Major Players (The Vegapunk Saga’s Setup)
- 2.04: The Space Race (Evidence for the Moon Arc)
- 2.05: History Repeating (Sky Island Saga Parallels)
- 2.05.01: Proof of a World in the Sky
- 2.05.02: Unexpected Passenger
- 2.05.03: Skill Demonstration
- 2.05.04: Expert Help
- 2.05.05: The Saboteur
- 2.05.06: Guiding Bird
- 2.05.07: First Encounter
- 2.05.08: God’s Army
- 2.05.09: War for the Land
- 2.05.10: Klabautermann
- 2.05.11: Investigation
- 2.05.12: Object of Desire
- 2.05.13: Hint to the Void Century
- 2.05.14: The True Story
- 2.05.15: The Final Battle
- 2.05.16: Return and Enemy Retreat
- 2.06: Post-Moon Arc (Monet’s Recruitment)
- 2.07: Chapter 2 Summary
- Chapter 3: The Monet Retrieval Arc (Monet's Backstory)
- 3.01: What We Know
- 3.02: The Missing Races
- 3.02.01: The Winged Race
- 3.02.02: Trimming the Possibilities
- 3.02.03: The Reptilian Race
- 3.03: Monet and the Medusa Pirates
- 3.04: The Minoa Arc (Monet’s Departure)
- 3.05: Chapter 3 Summary
- Chapter 4: Conclusions
- 4.01: Going Forward
- 4.02: Executive Summary
- 4.03: Final Thoughts
Hello, everyone!
I was actually planning to hold off on this one for a while, but since I've started talking about Monet again, I've been getting questions about how she may return, what connection she has to the rest of the story, and what role she would play going forward if she did, so I've decided to go ahead and address all of those questions at once. I've also been getting a lot of naysayers who aren't already familiar with a lot of the background information of Monet theories, so rather than explain it from scratch every single time, I want to have a summary of all of the most important details available to me at any given time.
I will say now that a lot of this has been covered in the past by other people and myself, so if you want to look over other people's interpretations or even my older ones, here are some links you may find helpful: Syphin's There's Something About Monet, Zaz's Snow White theory, Montblanc Noland's Laputa theory, Lokiz's True History of Monet, Van Reich's Home of a Harpy, Zero Zero no Mi's 325 All Known Possibilities, and my litany of theories (Straight to the Moon, To the Moon and Back, The Final Devil Fruit of the Straw Hats, What We Know and What We Assume We Know, Monet and the Birdfolk, Fight or Flight, Over the Rainbow, Who Will Tell Your Story, Piracy on a Budget, and of course all of the Female Recruitment theories I've been posting so fervently recently). I will not be referencing all of these theories within this one, as many of them are out of date or have had many of their aspects debunked, including a handful of mine, but it's nice to be able to look back on the history of Monet theories, and even the ones that have been debunked can be used to inform or inspire new conclusions. The goal for today is to build on that history, modernize the perspective on the previous evidence, possibly come to new conclusions not already suggested, and most importantly, to compile the evidence into one easily accessible place. Whatever conclusions or predictions we make today, you are absolutely free to ignore or disagree with, just please base your conclusion off of the evidence available. If somehow I miss any evidence, please do not hesitate to let me know and I may add it in.
So now, without further ado, let's begin.
To start, I'd like to review the reasons why people believe Monet is alive, and by extension, why they believe she's going to relevant to the main plot and potentially even join the Straw Hat Crew. This list may not end up being exhaustive, so again, if I miss anything let me know, but these are the most important or common bits that I could find or remember. I'll try to list them in order of relevance from greatest to least:
After being launched by Luffy, Caesar ends up on the dock behind the lab, where he musters the strength to get the last laugh by stabbing Smoker's heart with a piece of shrapnel presumably torn from the metal of the lab's walls on his flight out. Of course, as we know, it is actually Monet's heart, as she coughs up blood and examines her chest, feeling the pain of the wound, moments before collapsing. Notice, though, that the next time we see Caesar, he is completely unconscious, with the heart and the shrapnel next to him. Curiously, though, the shrapnel is not buried into the heart as we see previously, but into the dock. Did Caesar stab once and then pull the shrapnel out to try again, only to miss the second time? Perhaps, but notice how shaky his hand is in the second panel. I believe that Caesar used the last of his energy on this action, and passed out before he could confirm what had happened.
We do know for a fact that the shrapnel hit in the first place, though, as Monet coughs up blood and passes out, and the heart itself is bleeding and does appear deformed where the shrapnel is hitting it. However, that deformation is a somewhat odd detail in and of itself. If the shrapnel were simply piercing the heart, I would think that it would just go straight in, and the deformation would be a superfluous visual detail. I believe that deformation is implying a slight angle to the point of entry, which resulted in the shrapnel slipping off of it and into its final destination of the dock. The shrapnel was sharp, of course, so it did cut the heart, and there was certainly enough force for the heart to feel impact, but as we've seen with other hearts (Law's in particular), an impact is enough to cause one to cough up blood and pass out, but not necessarily kill them.
No blood on his mouth before being hit, instant knockout and bleeding when he is. Law does recover pretty quickly here, though, likely in part due to being prepared for the impact while Monet was taken completely off guard, but getting slashed across the heart probably didn't help her either. The point being that nothing we were shown with Monet was inconsistent with any other instance of damage incurred via Law's ability.
I have received many counterarguments for this over the years, most of which I don't consider to be valid, but I'll go over them now anyway just to be thorough.
"But the anime shows the shrapnel buried in the heart, and we watch it stop beating!" The anime also has Chopper eating three Rumble Balls within an hour during the Davy Back Fight with no repercussions, I don't think Toei is really too concerned with planning ahead for developments that weren't explicitly established. As far as I know, the only involvement Oda has with the production of the anime at all is when Toei wants to make original Devil Fruit users but don't want to risk stepping on Oda's toes. This one tiny panel implying that Monet is alive is super easy to miss, to the point that Toei doesn't even include the heart in that same scene in the anime. I'm not willing to put the anime's interpretation of events over the original author's. Furthermore, it'd be super easy to explain away later anyway: Caesar lost consciousness as he stabbed at the heart, and we were seeing his interpretation of events. Sure, it being a hallucination is a bit of a cop out, but that's what Toei gets for not reading closely.
"Maybe Oda made a mistake." This one's just insulting. Oda makes mistakes, sure, like leaving out scars here and there or making Arlong's teeth smooth instead of sharp that one time, but any mistakes that actually impact the plot, he corrects by the time the collected volumes come out. Jozu losing his arm and seemingly growing it back after the Summit War? Removed again in the volume. Katakuri having a Logia Fruit? Oops, it's a Special Paramecia. Monet's heart? Never re-stabbed. Not in the collected volume, not in the official digital colored version, never. More importantly, though, how would Oda make this mistake? As far as I'm aware, Oda has always drawn traditionally, not digitally, so it's definitely not a layering error. Even if he had an assistant do that panel, which again, Oda doesn't tend to do, the assistant would also have been under the impression that Monet's heart was supposed to be pierced. It just isn't a mistake that makes any sense to be made. There's also the fact that this isn't the first time Oda's done something like this: earlier that same arc, in the cover story arc reviewing the status of the extended cast post timeskip, we see that someone has left three sake cups and an article about the Straw Hats' return on Ace's grave.
The only people who would know the significance of sharing three cups of sake with Ace are Luffy, who is obviously preoccupied at this point in the story, and Sabo, who at the time we all had been told was dead. For many people, this was the moment that convinced them that Sabo was, in fact, alive, which we found out to be the case 67 chapters later. Oda is clearly no stranger to leaving hints that a deceased character is alive, and introducing the idea of implied survival in the same arc as another example seems a bit too on the nose to be a coincidence to me. This also leads me to my next point...
"The Vivre Card Databook says that Monet is dead!" And Sabo's entry in Green said he was too. Go figure, Oda doesn't want to spoil his own series. If you must insist that the databooks are infallible and 100% truthful, I'll note that her entry doesn't actually say she's dead like any given confirmed dead character's, rather just that she was pierced through the heart, which only implies death, leaving the door open for it to be revealed later that she's alive.
"Monet still probably died from the Shinokuni gas spilling in / she bled out / she died of something else." Then why didn't Oda just commit to her being stabbed? We know her heart was wounded, but Oda reneged on that by showing us that her heart wasn't pierced as a subtle plot twist. Why would he show us that just to have it turn out that something he didn't even allude to happened to her instead when he could just have left her being stabbed? It doesn't make any narrative sense, and would be sloppy at best and mean-spirited at worst. Also, I'd like to point out that Monet's location, C Block, was explicitly shown not to have filled with Shinokuni.
Presumably it was sealed tight, protecting her from the gas, but even if it wasn't and she ended up coated in Shinokuni, that doesn't really mean anything, as we'll go over later. The point right now is that there's no good reason to assume that Monet died of some currently unexplained event when we were told she survived the stabbing that we were supposed to believe killed her.
"If Oda was going to bring Monet back, he would have done it by now!" How long was it between Jinbe's invitation and official recruitment? 328 chapters, 648-976. Heck, how long was it between the first time his name was mentioned and his first appearance? 458, 69-528, a span of over ten years of publication. How long ago was Vegapunk first mentioned, and we still haven't even seen his face yet? 547 chapters ago at the time of this writing, back in 433! Oda likes to play the long game. Oda also once said in an interview at Jump Festa 2018 that while he doesn't necessarily plan for every character to come back, he keeps characters alive for the sake of having the possibility for them to return. One may take this to mean that he isn't actually planning for Monet to come back, but given the fact that she's one of the few characters he showed being killed only to hint that she's still alive tells me that he has a specific plan for her. The latter half of this theory will be dedicated to my thoughts on what that plan may be, but for now, let's just focus on the fact that he created the opportunity for her to return, and most likely plans to use it.
"Just cus she's alive doesn't mean she's joining the crew." Yes, true, but also irrelevant, because we're talking about her being alive, which this argument acknowledges, so I'm calling that a win.
What an odd detail to hide behind a speech bubble and then never acknowledge in any way shape or form, especially since later on in the very same page, we see Monet in a different scene (as evidenced by her different outfit) with the tattoo mysteriously missing. In fact, every time we've seen Monet with her human limbs, we either see her from the left with no tattoo or she has long sleeves. Oda clearly didn't want us to see that tattoo with any particular detail, as he could easily have let her have it in any of those panels. He also could just as easily have drawn her arm slightly off panel, hiding the tattoo but demonstrating that she still has it, but no, he shows it completely gone. Perhaps Monet covered it with makeup, or shapeshifted it off with her Logia ability? But why would she do that? Or better yet, why didn't she do that earlier? The only thing we know for sure is that she definitely doesn't have it anymore now that she has wings instead of her original arms. The fact that Oda showed us it exists only to subsequently scrub its presence from all subsequent panels (not unlike how he's currently treating Monet) tells us that that tattoo holds significance, presumably in the form of allegiance or affiliation to someone. I've seen it suggested that it's a derivation of the Beasts Pirates Jolly Roger, but I don't personally think it looks much like it or any other Jolly Roger we've ever seen. There was once a time where people thought it was somehow related to the heart tattoo that Big Mom has on her left arm, and that perhaps Monet was one of Big Mom's daughters, but we have all 39 of them accounted for at this point. I've also seen it suggested that it's related to her "misfortunate environment," and much like the Hoof of the Flying Dragon, it could be a brand that she wants to hide because she doesn't like to remember it. But then why would she not have it hidden before? My best guess is that one of the children pointed it out and it either upset her or she didn't want the children to know what it was, so she hid it from that point on. Either way, Oda clearly wants us to know about the tattoo's existence, but he doesn't want us to know anything about it just yet. It may also serve as a parallel to Nami, who also had a tattoo associated with her past on her left arm that, out of shame, she attempted to destroy and then ultimately had removed and covered up.
Speaking of character details on Monet's limbs...

After being launched by Luffy, Caesar ends up on the dock behind the lab, where he musters the strength to get the last laugh by stabbing Smoker's heart with a piece of shrapnel presumably torn from the metal of the lab's walls on his flight out. Of course, as we know, it is actually Monet's heart, as she coughs up blood and examines her chest, feeling the pain of the wound, moments before collapsing. Notice, though, that the next time we see Caesar, he is completely unconscious, with the heart and the shrapnel next to him. Curiously, though, the shrapnel is not buried into the heart as we see previously, but into the dock. Did Caesar stab once and then pull the shrapnel out to try again, only to miss the second time? Perhaps, but notice how shaky his hand is in the second panel. I believe that Caesar used the last of his energy on this action, and passed out before he could confirm what had happened.
We do know for a fact that the shrapnel hit in the first place, though, as Monet coughs up blood and passes out, and the heart itself is bleeding and does appear deformed where the shrapnel is hitting it. However, that deformation is a somewhat odd detail in and of itself. If the shrapnel were simply piercing the heart, I would think that it would just go straight in, and the deformation would be a superfluous visual detail. I believe that deformation is implying a slight angle to the point of entry, which resulted in the shrapnel slipping off of it and into its final destination of the dock. The shrapnel was sharp, of course, so it did cut the heart, and there was certainly enough force for the heart to feel impact, but as we've seen with other hearts (Law's in particular), an impact is enough to cause one to cough up blood and pass out, but not necessarily kill them.

No blood on his mouth before being hit, instant knockout and bleeding when he is. Law does recover pretty quickly here, though, likely in part due to being prepared for the impact while Monet was taken completely off guard, but getting slashed across the heart probably didn't help her either. The point being that nothing we were shown with Monet was inconsistent with any other instance of damage incurred via Law's ability.
I have received many counterarguments for this over the years, most of which I don't consider to be valid, but I'll go over them now anyway just to be thorough.
"But the anime shows the shrapnel buried in the heart, and we watch it stop beating!" The anime also has Chopper eating three Rumble Balls within an hour during the Davy Back Fight with no repercussions, I don't think Toei is really too concerned with planning ahead for developments that weren't explicitly established. As far as I know, the only involvement Oda has with the production of the anime at all is when Toei wants to make original Devil Fruit users but don't want to risk stepping on Oda's toes. This one tiny panel implying that Monet is alive is super easy to miss, to the point that Toei doesn't even include the heart in that same scene in the anime. I'm not willing to put the anime's interpretation of events over the original author's. Furthermore, it'd be super easy to explain away later anyway: Caesar lost consciousness as he stabbed at the heart, and we were seeing his interpretation of events. Sure, it being a hallucination is a bit of a cop out, but that's what Toei gets for not reading closely.
"Maybe Oda made a mistake." This one's just insulting. Oda makes mistakes, sure, like leaving out scars here and there or making Arlong's teeth smooth instead of sharp that one time, but any mistakes that actually impact the plot, he corrects by the time the collected volumes come out. Jozu losing his arm and seemingly growing it back after the Summit War? Removed again in the volume. Katakuri having a Logia Fruit? Oops, it's a Special Paramecia. Monet's heart? Never re-stabbed. Not in the collected volume, not in the official digital colored version, never. More importantly, though, how would Oda make this mistake? As far as I'm aware, Oda has always drawn traditionally, not digitally, so it's definitely not a layering error. Even if he had an assistant do that panel, which again, Oda doesn't tend to do, the assistant would also have been under the impression that Monet's heart was supposed to be pierced. It just isn't a mistake that makes any sense to be made. There's also the fact that this isn't the first time Oda's done something like this: earlier that same arc, in the cover story arc reviewing the status of the extended cast post timeskip, we see that someone has left three sake cups and an article about the Straw Hats' return on Ace's grave.

The only people who would know the significance of sharing three cups of sake with Ace are Luffy, who is obviously preoccupied at this point in the story, and Sabo, who at the time we all had been told was dead. For many people, this was the moment that convinced them that Sabo was, in fact, alive, which we found out to be the case 67 chapters later. Oda is clearly no stranger to leaving hints that a deceased character is alive, and introducing the idea of implied survival in the same arc as another example seems a bit too on the nose to be a coincidence to me. This also leads me to my next point...
"The Vivre Card Databook says that Monet is dead!" And Sabo's entry in Green said he was too. Go figure, Oda doesn't want to spoil his own series. If you must insist that the databooks are infallible and 100% truthful, I'll note that her entry doesn't actually say she's dead like any given confirmed dead character's, rather just that she was pierced through the heart, which only implies death, leaving the door open for it to be revealed later that she's alive.
"Monet still probably died from the Shinokuni gas spilling in / she bled out / she died of something else." Then why didn't Oda just commit to her being stabbed? We know her heart was wounded, but Oda reneged on that by showing us that her heart wasn't pierced as a subtle plot twist. Why would he show us that just to have it turn out that something he didn't even allude to happened to her instead when he could just have left her being stabbed? It doesn't make any narrative sense, and would be sloppy at best and mean-spirited at worst. Also, I'd like to point out that Monet's location, C Block, was explicitly shown not to have filled with Shinokuni.

Presumably it was sealed tight, protecting her from the gas, but even if it wasn't and she ended up coated in Shinokuni, that doesn't really mean anything, as we'll go over later. The point right now is that there's no good reason to assume that Monet died of some currently unexplained event when we were told she survived the stabbing that we were supposed to believe killed her.
"If Oda was going to bring Monet back, he would have done it by now!" How long was it between Jinbe's invitation and official recruitment? 328 chapters, 648-976. Heck, how long was it between the first time his name was mentioned and his first appearance? 458, 69-528, a span of over ten years of publication. How long ago was Vegapunk first mentioned, and we still haven't even seen his face yet? 547 chapters ago at the time of this writing, back in 433! Oda likes to play the long game. Oda also once said in an interview at Jump Festa 2018 that while he doesn't necessarily plan for every character to come back, he keeps characters alive for the sake of having the possibility for them to return. One may take this to mean that he isn't actually planning for Monet to come back, but given the fact that she's one of the few characters he showed being killed only to hint that she's still alive tells me that he has a specific plan for her. The latter half of this theory will be dedicated to my thoughts on what that plan may be, but for now, let's just focus on the fact that he created the opportunity for her to return, and most likely plans to use it.
"Just cus she's alive doesn't mean she's joining the crew." Yes, true, but also irrelevant, because we're talking about her being alive, which this argument acknowledges, so I'm calling that a win.
Although never alluded to or otherwise implied in series, Monet is revealed in an SBS to be fellow Donquixote Pirate Sugar's older sister, and the two of them were rescued from a "misfortunate environment" by Doflamingo thirteen years before the current storyline. That seems like an unusual amount of detail in Monet's story to just not be talked about at all. This woman is supposedly dead, and Doflamingo knows it, but we never see him break the news to her younger sister? The deep psychological reason that Senor Pink dresses like a literal baby is vital information, but who wants to see Sugar grieving (or potentially more interesting, dismissing) her deceased sister? Why even bother making them sisters if the narrative is just going to treat them like complete strangers? Also, whole lot of work must have gone into "a misfortunate environment," huh, Oda? Why come up with a sad backstory bogged down by boring details like Baby 5 being abandoned by her mother because she was too poor to feed her own daughter when you can just sum it up as misfortunate? Oda isn't that sloppy. If he didn't already have intentions to tell us the details later, he probably would have either just gone ahead and told us them right there, gone over it in the Vivre Card Databook like for other minor characters like Heracles, or acknowledged that he had no intention of doing so.
He also goes on to say that Doflamingo is the one who gave them their Devil Fruit, and that Doflamingo is observant of the environments that people grow up in. The wording of these two ideas implies that they're somehow related, as if Doflamingo specifically chose to give Monet a snow-based fruit and Sugar a youth/control-based fruit. Whether or not that's the case is hard to say, but it just seems odd to word it that way otherwise. Even if they're unrelated, Oda likely meant that Doflamingo singled them out from their environment to recruit them because he saw some kind of value in them and knew how to manipulate them to draw out that value. That manipulation may be evidenced through Monet's final words:
"[Doflamingo is going to be] the man who becomes Pirate King." Correct me if I'm wrong, but has Doflamingo ever mentioned any semblance of a desire to become Pirate King? The only character who ever implies any interest in making Doflamingo Pirate King is Monet herself, with no such ambition being mentioned by any other member of the Donquixote Pirates. If Doflamingo is in fact manipulating Monet, it's very possible that her impression that he wants to be Pirate King is a part of it. It's also possible that it's related to some greater ambition or dream that Monet has independently of Doflamingo himself, which is somehow contingent on him becoming Pirate King.
Whatever that greater ambition is, though, it hasn't been passed on to anyone else. Most if not every other major death in One Piece comes with some form of inherited will, an unfulfilled dream or desire taken on by a successor. Whether it's Kuina's dream to be the greatest swordsman inherited by Zoro, Hiriluk's dream to create the grand panacea inherited by Chopper, or Pedro's belief that the Straw Hats would bring about the Dawn of the World likely to be inherited by Carrot, death in One Piece is never the end of a person so long as someone is around to carry on what was important to them. A minor character like Mr. 11 back in Alabasta was never going to get anything like that, as he was a throwaway meant to show the cruelty of Baroque Works and to reintroduce Smoker and Tashigi back into the narrative, but Monet? With so many vague hints surrounding her past, many of which I haven't even touched on yet, I cannot imagine that Oda has no intentions of revealing Monet's ambitions to us sooner or later. What's more, if he was going to have someone else carry on that will, he probably would have established that anyone else even knows or cares that she's dead by now. The only person that's said anything about Monet dying is Doflamingo, and I'm pretty sure he just assumed that because she failed to hit the self destruct switch and then never reported back to him. Her own sister is never even shown to be aware of her demise, so either Doflamingo couldn't bring himself to tell her, or she just isn't interested in carrying on Monet's will or avenging her.
Another, possibly more subtle hint about her past comes from her fight with Zoro, as people also seem to strongly believe that the reason she froze up during his final attack is inherently tied to her backstory.
I think the logic is that it seems odd for her, a pirate who has probably been in life or death situations before, to be paralyzed in fear when facing a stronger opponent. Plus, it's not like she doesn't know how to fight strong people, she nearly beat Luffy by prioritizing strategy over force, so why isn't she acting just as pragmatic here and turning to snow and disappearing into the floor? The popular explanation is that she has some unexplored trauma and that either Zoro's words or his expression were a trigger that subconsciously brought her back to the event in question. I've always been willing to take it at face value that Zoro is just that intimidating, but it is presented a little strangely.
Possibly of less importance, there's also the fact that we most likely haven't learned her real name yet, as all of the members of the Doflamingo Pirates use codenames. I think that Rocinante and Vergo are the only ones whose names we actually learn, so maybe it doesn't really matter too much, but I feel like Oda must have a name in mind for her that he just hasn't decided to reveal to us yet, and I for one desperately want to know it. Quick aside, why haven't we been told Baby 5's real name yet? She's a part of the Grand Fleet, I feel like we deserve to know by now.
He also goes on to say that Doflamingo is the one who gave them their Devil Fruit, and that Doflamingo is observant of the environments that people grow up in. The wording of these two ideas implies that they're somehow related, as if Doflamingo specifically chose to give Monet a snow-based fruit and Sugar a youth/control-based fruit. Whether or not that's the case is hard to say, but it just seems odd to word it that way otherwise. Even if they're unrelated, Oda likely meant that Doflamingo singled them out from their environment to recruit them because he saw some kind of value in them and knew how to manipulate them to draw out that value. That manipulation may be evidenced through Monet's final words:

"[Doflamingo is going to be] the man who becomes Pirate King." Correct me if I'm wrong, but has Doflamingo ever mentioned any semblance of a desire to become Pirate King? The only character who ever implies any interest in making Doflamingo Pirate King is Monet herself, with no such ambition being mentioned by any other member of the Donquixote Pirates. If Doflamingo is in fact manipulating Monet, it's very possible that her impression that he wants to be Pirate King is a part of it. It's also possible that it's related to some greater ambition or dream that Monet has independently of Doflamingo himself, which is somehow contingent on him becoming Pirate King.
Whatever that greater ambition is, though, it hasn't been passed on to anyone else. Most if not every other major death in One Piece comes with some form of inherited will, an unfulfilled dream or desire taken on by a successor. Whether it's Kuina's dream to be the greatest swordsman inherited by Zoro, Hiriluk's dream to create the grand panacea inherited by Chopper, or Pedro's belief that the Straw Hats would bring about the Dawn of the World likely to be inherited by Carrot, death in One Piece is never the end of a person so long as someone is around to carry on what was important to them. A minor character like Mr. 11 back in Alabasta was never going to get anything like that, as he was a throwaway meant to show the cruelty of Baroque Works and to reintroduce Smoker and Tashigi back into the narrative, but Monet? With so many vague hints surrounding her past, many of which I haven't even touched on yet, I cannot imagine that Oda has no intentions of revealing Monet's ambitions to us sooner or later. What's more, if he was going to have someone else carry on that will, he probably would have established that anyone else even knows or cares that she's dead by now. The only person that's said anything about Monet dying is Doflamingo, and I'm pretty sure he just assumed that because she failed to hit the self destruct switch and then never reported back to him. Her own sister is never even shown to be aware of her demise, so either Doflamingo couldn't bring himself to tell her, or she just isn't interested in carrying on Monet's will or avenging her.
Another, possibly more subtle hint about her past comes from her fight with Zoro, as people also seem to strongly believe that the reason she froze up during his final attack is inherently tied to her backstory.

I think the logic is that it seems odd for her, a pirate who has probably been in life or death situations before, to be paralyzed in fear when facing a stronger opponent. Plus, it's not like she doesn't know how to fight strong people, she nearly beat Luffy by prioritizing strategy over force, so why isn't she acting just as pragmatic here and turning to snow and disappearing into the floor? The popular explanation is that she has some unexplored trauma and that either Zoro's words or his expression were a trigger that subconsciously brought her back to the event in question. I've always been willing to take it at face value that Zoro is just that intimidating, but it is presented a little strangely.
Possibly of less importance, there's also the fact that we most likely haven't learned her real name yet, as all of the members of the Doflamingo Pirates use codenames. I think that Rocinante and Vergo are the only ones whose names we actually learn, so maybe it doesn't really matter too much, but I feel like Oda must have a name in mind for her that he just hasn't decided to reveal to us yet, and I for one desperately want to know it. Quick aside, why haven't we been told Baby 5's real name yet? She's a part of the Grand Fleet, I feel like we deserve to know by now.
At several points throughout Punk Hazard, we see Monet's nose buried in stacks of books and papers, constantly taking notes and reading through her coke-bottle glasses. If one takes a closer look at the books surrounding her, though, we notice an interesting trend in the ones that are legible: they seem to be related to astronomy.
Reading right to left, in the first panel, we can very clearly see "ASTRO" and "LI," the former very likely being short for astronomy, astrology, or maybe even astrophysics. "LI" doesn't mean much on its own until the second panel, where we see another book of the same color at the same position in a stack placed at the exact same spot on the table relative to Monet that says "CLIP." Unless someone wrote a whole book on clipboards, I'm quite confident that this book is labeled "ECLIPSE," an astronomical phenomenon. The latter two books are much more difficult to discern, unfortunately, but the blue-ish book in the third panel appears to say "Anti", possibly "Antig," which may mean it is a book on antigravity. The final book, I can't make heads or tails of. I see OIKA, but I'm pretty sure that's not it, unless maybe it's in another language. I suppose it could be Greek since she's a harpy, but I don't know any Greek and that's just spitballing on my part. If you know Greek or can make out those letters at all, please let me know. I remember someone a few years ago suggesting she had a book labeled "Black," presumably short for Black Hole, but this is the only other book of hers that I was able to find, and it definitely doesn't say black hole.
Regardless of what the less legible books say, Oda put "ASTRO" and "CLIP" in big bold letters in plain view on two separate occasions. Why did Monet have books on astronomical events? Literally no one in the entire series has ever showed even a passing interest in astronomy, unless you count Enel literally absconding to the moon, the Oharans owning a geocentric globe model, or Drake being stated to like astrophysics, but none of those are the same. Enel doesn't care about the alignment of the stars and planets or anything, I don't think he even knows what those are, he just wanted to claim the largest expanse of land that he could for himself. The Oharans own a globe, sure, but they seem more interested in world history, and probably use it more for studying geography. Drake's interest in astrophysics, contrary to what its name implies, isn't concerned with the movement of astronomical bodies, but uses physics to determine their makeup. They're all related conceptually to astronomy, sure, but Monet is the only character shown to be studying astronomy itself, and for that information to be so casually yet so subtly presented to us must mean it is in some way significant. Many believe that the Straw Hats will go to the moon for one reason or another and either fight Enel again or reluctantly join forces with him to fight off aliens, and that since Monet is the only known astronomer in the series, she will likely somehow be related to the process of getting to the moon.

Reading right to left, in the first panel, we can very clearly see "ASTRO" and "LI," the former very likely being short for astronomy, astrology, or maybe even astrophysics. "LI" doesn't mean much on its own until the second panel, where we see another book of the same color at the same position in a stack placed at the exact same spot on the table relative to Monet that says "CLIP." Unless someone wrote a whole book on clipboards, I'm quite confident that this book is labeled "ECLIPSE," an astronomical phenomenon. The latter two books are much more difficult to discern, unfortunately, but the blue-ish book in the third panel appears to say "Anti", possibly "Antig," which may mean it is a book on antigravity. The final book, I can't make heads or tails of. I see OIKA, but I'm pretty sure that's not it, unless maybe it's in another language. I suppose it could be Greek since she's a harpy, but I don't know any Greek and that's just spitballing on my part. If you know Greek or can make out those letters at all, please let me know. I remember someone a few years ago suggesting she had a book labeled "Black," presumably short for Black Hole, but this is the only other book of hers that I was able to find, and it definitely doesn't say black hole.
Regardless of what the less legible books say, Oda put "ASTRO" and "CLIP" in big bold letters in plain view on two separate occasions. Why did Monet have books on astronomical events? Literally no one in the entire series has ever showed even a passing interest in astronomy, unless you count Enel literally absconding to the moon, the Oharans owning a geocentric globe model, or Drake being stated to like astrophysics, but none of those are the same. Enel doesn't care about the alignment of the stars and planets or anything, I don't think he even knows what those are, he just wanted to claim the largest expanse of land that he could for himself. The Oharans own a globe, sure, but they seem more interested in world history, and probably use it more for studying geography. Drake's interest in astrophysics, contrary to what its name implies, isn't concerned with the movement of astronomical bodies, but uses physics to determine their makeup. They're all related conceptually to astronomy, sure, but Monet is the only character shown to be studying astronomy itself, and for that information to be so casually yet so subtly presented to us must mean it is in some way significant. Many believe that the Straw Hats will go to the moon for one reason or another and either fight Enel again or reluctantly join forces with him to fight off aliens, and that since Monet is the only known astronomer in the series, she will likely somehow be related to the process of getting to the moon.

What an odd detail to hide behind a speech bubble and then never acknowledge in any way shape or form, especially since later on in the very same page, we see Monet in a different scene (as evidenced by her different outfit) with the tattoo mysteriously missing. In fact, every time we've seen Monet with her human limbs, we either see her from the left with no tattoo or she has long sleeves. Oda clearly didn't want us to see that tattoo with any particular detail, as he could easily have let her have it in any of those panels. He also could just as easily have drawn her arm slightly off panel, hiding the tattoo but demonstrating that she still has it, but no, he shows it completely gone. Perhaps Monet covered it with makeup, or shapeshifted it off with her Logia ability? But why would she do that? Or better yet, why didn't she do that earlier? The only thing we know for sure is that she definitely doesn't have it anymore now that she has wings instead of her original arms. The fact that Oda showed us it exists only to subsequently scrub its presence from all subsequent panels (not unlike how he's currently treating Monet) tells us that that tattoo holds significance, presumably in the form of allegiance or affiliation to someone. I've seen it suggested that it's a derivation of the Beasts Pirates Jolly Roger, but I don't personally think it looks much like it or any other Jolly Roger we've ever seen. There was once a time where people thought it was somehow related to the heart tattoo that Big Mom has on her left arm, and that perhaps Monet was one of Big Mom's daughters, but we have all 39 of them accounted for at this point. I've also seen it suggested that it's related to her "misfortunate environment," and much like the Hoof of the Flying Dragon, it could be a brand that she wants to hide because she doesn't like to remember it. But then why would she not have it hidden before? My best guess is that one of the children pointed it out and it either upset her or she didn't want the children to know what it was, so she hid it from that point on. Either way, Oda clearly wants us to know about the tattoo's existence, but he doesn't want us to know anything about it just yet. It may also serve as a parallel to Nami, who also had a tattoo associated with her past on her left arm that, out of shame, she attempted to destroy and then ultimately had removed and covered up.
Speaking of character details on Monet's limbs...
Why on Earth did Monet ask Law to make her into a Harpy? She wasn't disabled like the convicts and Brownbeard Pirates, so she didn't need the surgery. Did she just think it would be cool? That doesn't really seem to fit her personality very well. Does she just love birds that much? She did carry around an ornithology textbook in her youth, so maybe, but that's a pretty weak reason. Did she think it would be really efficient? Maybe, that fits a bit better, as it lets her travel more quickly and gather information more effectively, but it's also a pretty huge commitment to make just because it's handy. No, I think it's intrinsically tied to her backstory, possibly even tied to her unknown dream that I alluded to earlier. Again, since Oda didn't take the time to elaborate on her reasoning in her Vivre Card entry, we can infer that he must not be ready to tell us about it yet.
I said earlier it didn't matter whether Monet got hit with Shinokuni, and here's why. After the Straw Hats left Punk Hazard, the survivors of G-5 and Brownbeard's men donned protective gear designed by Vegapunk (making it effective against Caesar's gas weapons) to venture back through the lab and the rest of the island to release as many people as they could from the shells encasing them.
As Smoker points out, this is the only exit from the lab, presumably meaning the only one with access to any ships at the moment and not covered in Shinokuni, so anyone that the search team found would need to be brought through that opening. If the room that Monet was in wasn't sealed off from Shinokuni and the gas was able to seep in to get her, then most likely they would have found and retrieved her so as to arrest her. I suppose they could have left her to die, but as we established earlier, even that wouldn't necessarily be a death sentence, as Oda has already jumped through hoops to keep her alive. Therefore, if G-5 found Monet, then she was most likely on board the tanker with Smoker, Tashigi, G-5, and the children heading towards Vegapunk for treatment, which would allow her to be treated for Shinokuni poisoning if necessary. What would happen to Monet would be up in the air after that, but she'd be alive and capable of returning through some narrative sequence later, but again, that's a discussion for later.
If C Block was completely sealed and G-5 wasn't able to find Monet, then that means she hasn't been arrested and is still free to roam, though she'd need to regain consciousness first. Presumably the biting cold of Punk Hazard wouldn't damage her heart, considering that she's made of snow, so as long as the wound scabbed over (and let's face it, worse wounds have been sustained without treatment in One Piece), it's not too hard to imagine her getting up on her own at some point. From there, she'd just need to find her heart through some means after wandering through the abandoned facility (presumably following where there isn't toxic gas), and then decide how to proceed. What her thought process would be is currently unknowable, but her ability to fly would probably make getting to somewhere like Dressrosa easy enough, since Doflamingo and Buffalo were able to travel between the two without seeming to need any particular navigational items. Even Caesar planned to fly to Dressrosa in gas form, so clearly the two can reach other through an established straight line. She also could have been found by Kuzan, who may have scooped her up to take to Blackbeard because of her Devil Fruit, but it's hard to say if Kuzan knew about her at all.
Regardless of which path Oda takes, the search team finding or passing over Monet, Monet has a method for being reintroduced to the plot whenever Oda deems it appropriate, whether it be through a cover story or series proper.

As Smoker points out, this is the only exit from the lab, presumably meaning the only one with access to any ships at the moment and not covered in Shinokuni, so anyone that the search team found would need to be brought through that opening. If the room that Monet was in wasn't sealed off from Shinokuni and the gas was able to seep in to get her, then most likely they would have found and retrieved her so as to arrest her. I suppose they could have left her to die, but as we established earlier, even that wouldn't necessarily be a death sentence, as Oda has already jumped through hoops to keep her alive. Therefore, if G-5 found Monet, then she was most likely on board the tanker with Smoker, Tashigi, G-5, and the children heading towards Vegapunk for treatment, which would allow her to be treated for Shinokuni poisoning if necessary. What would happen to Monet would be up in the air after that, but she'd be alive and capable of returning through some narrative sequence later, but again, that's a discussion for later.
If C Block was completely sealed and G-5 wasn't able to find Monet, then that means she hasn't been arrested and is still free to roam, though she'd need to regain consciousness first. Presumably the biting cold of Punk Hazard wouldn't damage her heart, considering that she's made of snow, so as long as the wound scabbed over (and let's face it, worse wounds have been sustained without treatment in One Piece), it's not too hard to imagine her getting up on her own at some point. From there, she'd just need to find her heart through some means after wandering through the abandoned facility (presumably following where there isn't toxic gas), and then decide how to proceed. What her thought process would be is currently unknowable, but her ability to fly would probably make getting to somewhere like Dressrosa easy enough, since Doflamingo and Buffalo were able to travel between the two without seeming to need any particular navigational items. Even Caesar planned to fly to Dressrosa in gas form, so clearly the two can reach other through an established straight line. She also could have been found by Kuzan, who may have scooped her up to take to Blackbeard because of her Devil Fruit, but it's hard to say if Kuzan knew about her at all.
Regardless of which path Oda takes, the search team finding or passing over Monet, Monet has a method for being reintroduced to the plot whenever Oda deems it appropriate, whether it be through a cover story or series proper.
The fact that Monet is a villain has been a major source of contention on both sides of the argument, with the supporters claiming that she's no different conceptually from Nami and Robin, and the opponents claiming that Nami and Robin both showed good traits, such as Nami's refusal to hurt the innocent and Robin's attempts to help the Straw Hats and even saving Luffy, while Monet has been shown to be sadistic and cruel. Obviously I fall into the former camp, in no small part because Monet's good traits are given several opportunities to shine through, they're just deliberately set up to look bad in context. Remember, Robin providing a safe shortcut to Alabasta was implied to be sinister, but looking back it seems pretty likely she was trying to sabotage Crocodile.
If you pay attention to her dialogue, Monet is surprisingly caring given the company she keeps. Not only does she consistently express concern for the well-being of Caesar's subordinates when he tries to leave them for dead for his own ends, she also seems to legitimately worry about Law when his heart is damaged (although this one may be facetious since she already knows he's a traitor from spying on him and Luffy), and is also the one who suggested that Law help the poison victims by replacing their disabled legs.
That last one is of particular importance, because despite the fact that all of the victims had already been "saved" and swore undying loyalty to Caesar, she still wanted them to be healed, to be able to walk of their own power again. Maybe that was just pragmatism, but how dreary to write off a character's kindness as something so calculating. Perhaps if that were the only implication I could understand, but her relationship with the children backs up this idea.
While it's easy to argue that Monet was kind to the children as a part of the ruse, it's undeniable that she treated them well, providing as much for them as possible and leaving them wanting for nothing. While Mocha still trusting Monet even after learning the truth can be written off as her thinking that Monet was being tricked as well...
...Monet's attitude towards the possibility of the children being taken away is much harder to ignore.
She consistently refers to the children as her own, or to herself as their parent, despite the fact that the children aren't in the room and talking that way around strangers would simply be performative if not genuine. Though the first instance at first seems sarcastic, it is the second, in which she flies into a rage at the idea of having the children stolen from her, that truly informs every other action she has taken.
But now let us address the elephant in the room; why did Monet go along with poisoning the children? A longstanding argument has been that she wasn't actually aware of what exactly was in the candy that she was giving to the children or how dangerous it was, evidenced by the discussion that Momonosuke happens to catch while eavesdropping on Caesar.
Why would Caesar feel the need to explain that the children will die within the next few years from to exposure to the drugs to Monet if she already knows? The common explanation is that Oda has characters explain things that other characters already know all the time as a narrative device for the audience to get caught up, and honestly that's probably what was happening here. Regardless of the meaning of this scene in particular, I don't personally think it's necessary for understanding Monet's motivations within this arc.
Looking at the situation completely at face value, the simple answer to her complicity would be because it's all part of her job and she doesn't care. But let's read between the lines a little bit. Monet was sent to Punk Hazard to both spy on Caesar and ensure his research continues without a hitch. We know as much because Monet tells us so on a couple occasions.
If she fails in this duty, Doflamingo will kill her. Just from that, some people have concluded that she's just trying to survive no matter what, a bit of a more extreme case of exactly what Robin did: survive even at the expense of others' lives, but in this case, some of those lives are children. I think that is absolutely a part of it, but it's not the whole story. Consider for a moment the circumstances of the Punk Hazard arc. Law and Luffy are trying to take Caesar so as to interrupt Doflamingo's dealings with Kaido. More specifically, they're attempting to shut down Caesar's SAD production, which will halt the cultivation of SMILEs. The children, the test subjects of the gigantification project, are completely unrelated to the SMILEs, and instead are a part of the research conducted through Big Mom's funds. In short, Monet, an agent of Doflamingo, has no reason to protect the experiments that serve no purpose to Doflamingo. And yet, is she not justified? The letter of the law here is that she's to protect "Caesar and his experiments," and Vergo's already heading off to protect the SAD, so shouldn't someone think of the children? One could argue that protecting the children does protect Caesar, as losing the research related to them would incur Big Mom's wrath, but based on how Monet talks, I don't think that's her reasoning. Given the circumstances, I think she's walking a delicate tightrope between the dichotomy of her own ideals.
Monet has been instructed by Doflamingo, her savior and master, to protect Caesar and his research. Caesar's research involves harming children. If she stands against this, she stands against her savior and risks death. This is a non-option for her, but she can't just let children suffer, not the way she has. The children are going to die. This is, from her perspective, an inescapable truth, but must they feel pain as well? If they have a few years left to live, why can't they be happy? We've already seen hints that Monet is caring enough to ease the suffering of the convicts affected by Caesar's poison, wouldn't it also make sense that she'd want to do the same for helpless and deceived children?
Monet was not lying when she said she gave them everything they wanted. As I mentioned earlier, even after learning the truth about Caesar and the candy, Mocha believed in Monet, because Monet had never given her any reason to think that she would go along with such a heinous plot. The naivete of a child? Perhaps. But I think that the text speaks for itself when it presents Monet as jealously guarding "her" children that she's poured real time and effort into caring for. Even if Monet was cold and calculating in her perfect facade at first, her completely unnecessary and rage-fueled defense of an experiment unrelated to her master's wishes speaks volumes to her current feelings on the children. Whether she came to love them as her own over time or fell into the role instantly, I don't think it's too much of a stretch to say that Monet did her best to give them as good of lives as possible in the short amount of time they had remaining. Whether Monet was morally in the wrong for going along with Caesar's actions is not up for debate: she was. But was Robin in the right for working as an assassin and killing countless people, helping to facilitate a civil war within an otherwise peaceful nation just for the chance to learn forgotten history? Is Monet easing the suffering of children that she sees as doomed any less moral than Robin consigning countless children to be orphaned, or worse, to enlist in a war that shouldn't be happening in the first place, all in the pursuit of knowledge? I am not disparaging Robin or her character, I am only saying that whatever chance or benefit of the doubt we as readers gave to Robin when she first asked to join the crew, it isn't unreasonable to offer that same courtesy to Monet when we don't necessarily have all of the facts of her circumstances.
There's also subtle implications that Monet is somewhat merciful, or at least hesitant to kill if she can avoid it. Not only did she miss anything vital when attacking Robin, despite having the perfect opportunity to kill her, but in her fight against Luffy, she deliberately used an attack that doesn't cause pain and puts the opponent to sleep. Granted, in context, she knew she couldn't beat him in a contest of strength, so perhaps it was more strategic than anything, but for her to even know she has a technique like that implies that she isn't always going for lethal force in battle. Furthermore, she also may be the reason that Viola wasn't killed during the coup on Dressrosa, as she captured her and knew she had an ability that may be useful to Doflamingo.
Again, it seems like it's strategic, but just like with the children, she may have grown somewhat attached and come up with a way to protect her friend. The narrative has set up her character in such a way that all of her actions could be taken either way depending on how you look at it.
Even if I'm way off base, and Monet is truly cold and purely sadistic, I don't honestly see why that has to be a disqualifying factor. It would be an interesting change of pace from Nami and Robin's personality types, and more importantly, there's a huge swath of fans that strongly believe Caesar is going to join the crew, and between the two, he's the one that we know for a fact reveled in playing with those children's lives. I'm not saying they're wrong, I just feel that if someone is pro-Caesar and anti-Monet, they had better have a stronger reason against her than her personality, because clearly that isn't a real issue for them.
If you pay attention to her dialogue, Monet is surprisingly caring given the company she keeps. Not only does she consistently express concern for the well-being of Caesar's subordinates when he tries to leave them for dead for his own ends, she also seems to legitimately worry about Law when his heart is damaged (although this one may be facetious since she already knows he's a traitor from spying on him and Luffy), and is also the one who suggested that Law help the poison victims by replacing their disabled legs.

That last one is of particular importance, because despite the fact that all of the victims had already been "saved" and swore undying loyalty to Caesar, she still wanted them to be healed, to be able to walk of their own power again. Maybe that was just pragmatism, but how dreary to write off a character's kindness as something so calculating. Perhaps if that were the only implication I could understand, but her relationship with the children backs up this idea.
While it's easy to argue that Monet was kind to the children as a part of the ruse, it's undeniable that she treated them well, providing as much for them as possible and leaving them wanting for nothing. While Mocha still trusting Monet even after learning the truth can be written off as her thinking that Monet was being tricked as well...

...Monet's attitude towards the possibility of the children being taken away is much harder to ignore.

She consistently refers to the children as her own, or to herself as their parent, despite the fact that the children aren't in the room and talking that way around strangers would simply be performative if not genuine. Though the first instance at first seems sarcastic, it is the second, in which she flies into a rage at the idea of having the children stolen from her, that truly informs every other action she has taken.
But now let us address the elephant in the room; why did Monet go along with poisoning the children? A longstanding argument has been that she wasn't actually aware of what exactly was in the candy that she was giving to the children or how dangerous it was, evidenced by the discussion that Momonosuke happens to catch while eavesdropping on Caesar.

Why would Caesar feel the need to explain that the children will die within the next few years from to exposure to the drugs to Monet if she already knows? The common explanation is that Oda has characters explain things that other characters already know all the time as a narrative device for the audience to get caught up, and honestly that's probably what was happening here. Regardless of the meaning of this scene in particular, I don't personally think it's necessary for understanding Monet's motivations within this arc.
Looking at the situation completely at face value, the simple answer to her complicity would be because it's all part of her job and she doesn't care. But let's read between the lines a little bit. Monet was sent to Punk Hazard to both spy on Caesar and ensure his research continues without a hitch. We know as much because Monet tells us so on a couple occasions.

If she fails in this duty, Doflamingo will kill her. Just from that, some people have concluded that she's just trying to survive no matter what, a bit of a more extreme case of exactly what Robin did: survive even at the expense of others' lives, but in this case, some of those lives are children. I think that is absolutely a part of it, but it's not the whole story. Consider for a moment the circumstances of the Punk Hazard arc. Law and Luffy are trying to take Caesar so as to interrupt Doflamingo's dealings with Kaido. More specifically, they're attempting to shut down Caesar's SAD production, which will halt the cultivation of SMILEs. The children, the test subjects of the gigantification project, are completely unrelated to the SMILEs, and instead are a part of the research conducted through Big Mom's funds. In short, Monet, an agent of Doflamingo, has no reason to protect the experiments that serve no purpose to Doflamingo. And yet, is she not justified? The letter of the law here is that she's to protect "Caesar and his experiments," and Vergo's already heading off to protect the SAD, so shouldn't someone think of the children? One could argue that protecting the children does protect Caesar, as losing the research related to them would incur Big Mom's wrath, but based on how Monet talks, I don't think that's her reasoning. Given the circumstances, I think she's walking a delicate tightrope between the dichotomy of her own ideals.
Monet has been instructed by Doflamingo, her savior and master, to protect Caesar and his research. Caesar's research involves harming children. If she stands against this, she stands against her savior and risks death. This is a non-option for her, but she can't just let children suffer, not the way she has. The children are going to die. This is, from her perspective, an inescapable truth, but must they feel pain as well? If they have a few years left to live, why can't they be happy? We've already seen hints that Monet is caring enough to ease the suffering of the convicts affected by Caesar's poison, wouldn't it also make sense that she'd want to do the same for helpless and deceived children?
Monet was not lying when she said she gave them everything they wanted. As I mentioned earlier, even after learning the truth about Caesar and the candy, Mocha believed in Monet, because Monet had never given her any reason to think that she would go along with such a heinous plot. The naivete of a child? Perhaps. But I think that the text speaks for itself when it presents Monet as jealously guarding "her" children that she's poured real time and effort into caring for. Even if Monet was cold and calculating in her perfect facade at first, her completely unnecessary and rage-fueled defense of an experiment unrelated to her master's wishes speaks volumes to her current feelings on the children. Whether she came to love them as her own over time or fell into the role instantly, I don't think it's too much of a stretch to say that Monet did her best to give them as good of lives as possible in the short amount of time they had remaining. Whether Monet was morally in the wrong for going along with Caesar's actions is not up for debate: she was. But was Robin in the right for working as an assassin and killing countless people, helping to facilitate a civil war within an otherwise peaceful nation just for the chance to learn forgotten history? Is Monet easing the suffering of children that she sees as doomed any less moral than Robin consigning countless children to be orphaned, or worse, to enlist in a war that shouldn't be happening in the first place, all in the pursuit of knowledge? I am not disparaging Robin or her character, I am only saying that whatever chance or benefit of the doubt we as readers gave to Robin when she first asked to join the crew, it isn't unreasonable to offer that same courtesy to Monet when we don't necessarily have all of the facts of her circumstances.
There's also subtle implications that Monet is somewhat merciful, or at least hesitant to kill if she can avoid it. Not only did she miss anything vital when attacking Robin, despite having the perfect opportunity to kill her, but in her fight against Luffy, she deliberately used an attack that doesn't cause pain and puts the opponent to sleep. Granted, in context, she knew she couldn't beat him in a contest of strength, so perhaps it was more strategic than anything, but for her to even know she has a technique like that implies that she isn't always going for lethal force in battle. Furthermore, she also may be the reason that Viola wasn't killed during the coup on Dressrosa, as she captured her and knew she had an ability that may be useful to Doflamingo.

Again, it seems like it's strategic, but just like with the children, she may have grown somewhat attached and come up with a way to protect her friend. The narrative has set up her character in such a way that all of her actions could be taken either way depending on how you look at it.
Even if I'm way off base, and Monet is truly cold and purely sadistic, I don't honestly see why that has to be a disqualifying factor. It would be an interesting change of pace from Nami and Robin's personality types, and more importantly, there's a huge swath of fans that strongly believe Caesar is going to join the crew, and between the two, he's the one that we know for a fact reveled in playing with those children's lives. I'm not saying they're wrong, I just feel that if someone is pro-Caesar and anti-Monet, they had better have a stronger reason against her than her personality, because clearly that isn't a real issue for them.
As soon as Monet's Devil Fruit was revealed, this one seemed to be the clincher for a lot of Monet for Next Straw Hat fans (ironically, not including me, I wasn't nearly as invested back in 2012 and I didn't understand the hype yet, naive child that I was). There was already a bit of buzz about the possibility of Monet joining because she was the first female subordinate to an arc villain in the New World and a certain unexplained event that I'll touch on shortly, but for that lady to be made of snow of all things? That set off more alarm bells than Brook revealing he was a musician.
For anyone unaware, Luffy loves snow. It's one of his favorite things after adventuring and meat. Luffy wants to see snow at pretty much all times, and will always get excited at the prospect of an island having snow.
On multiple occasions, Luffy has expressed a desire for the next island to have snow, and when he gets what he wants, he couldn't be happier. Sure, Nami theoretically could just make snow wherever, but there's never really been much of an issue with some overlap in abilities here and there (ie. Sanji and Luffy both being able to ignite their bodies, Zoro and Brook being swordsmen, Usopp and Franky having long-ranged weaponry, etc.), and I imagine that a Logia Devil Fruit focused specifically on snow would not only have a greater output than the Clima-Tact but would also be much easier to clean up since Monet would have complete control of it and could reabsorb the snow or otherwise cause it to disappear. It really isn't hard to imagine that Luffy would invite Monet to the crew over something so simple, regardless of any skills she may have, as he invited Chopper because he was cool rather than because he was a doctor.
The obvious counterargument would be that Luffy fought Monet and didn't seem to have any particular impression of her having snow powers. People have brushed this aside due to Luffy either being too preoccupied with the battle to make a note of something like that or just not realizing exactly what her ability was in the first place. Regardless of the reason he didn't bring it up at the time, if presented with the opportunity to recruit a person made of snow in a calmer scenario, I'm confident Luffy would take it. It also doesn't hurt that from a narrative perspective, Logia is the only Devil Fruit type not yet represented among the crew, so its element might as well be one that would make Luffy happy. Some people have suggested that the Snow-Snow Fruit will be used within the Straw Hat Crew, just not by Monet, with her death allowing the Snow-Snow Fruit to become available for another recruit or possibly Nami later, but as we've established, she is almost certainly not dead, so I'm not going to entertain the thought any further.
For anyone unaware, Luffy loves snow. It's one of his favorite things after adventuring and meat. Luffy wants to see snow at pretty much all times, and will always get excited at the prospect of an island having snow.

On multiple occasions, Luffy has expressed a desire for the next island to have snow, and when he gets what he wants, he couldn't be happier. Sure, Nami theoretically could just make snow wherever, but there's never really been much of an issue with some overlap in abilities here and there (ie. Sanji and Luffy both being able to ignite their bodies, Zoro and Brook being swordsmen, Usopp and Franky having long-ranged weaponry, etc.), and I imagine that a Logia Devil Fruit focused specifically on snow would not only have a greater output than the Clima-Tact but would also be much easier to clean up since Monet would have complete control of it and could reabsorb the snow or otherwise cause it to disappear. It really isn't hard to imagine that Luffy would invite Monet to the crew over something so simple, regardless of any skills she may have, as he invited Chopper because he was cool rather than because he was a doctor.

The obvious counterargument would be that Luffy fought Monet and didn't seem to have any particular impression of her having snow powers. People have brushed this aside due to Luffy either being too preoccupied with the battle to make a note of something like that or just not realizing exactly what her ability was in the first place. Regardless of the reason he didn't bring it up at the time, if presented with the opportunity to recruit a person made of snow in a calmer scenario, I'm confident Luffy would take it. It also doesn't hurt that from a narrative perspective, Logia is the only Devil Fruit type not yet represented among the crew, so its element might as well be one that would make Luffy happy. Some people have suggested that the Snow-Snow Fruit will be used within the Straw Hat Crew, just not by Monet, with her death allowing the Snow-Snow Fruit to become available for another recruit or possibly Nami later, but as we've established, she is almost certainly not dead, so I'm not going to entertain the thought any further.
I personally think this is one of the weaker pieces of evidence because its connection is by far the most speculative, but it's one that people tend to bring up a lot, and it is far too suspicious for me to comfortably brush off. After shipping off from Punk Hazard towards Dressrosa, there's a seemingly arbitrary shot of the Thousand Sunny sliding down a sloping wave, and beneath that wave is a horde of what appear to be giant sea rabbits. This is never acknowledged by the crew, it's just wordlessly presented to the audience (except apparently in the anime, but we all know by now how I feel about using the anime as a primary source). This scene wouldn't really stand out much if not for two factors: for one, the rabbits look strikingly similar to Monet's Snow Rabbit attack, a technique that seems somewhat out of place in her moveset as a whole, and which was introduced only a few chapters earlier.
Perhaps it's just a coincidence, or perhaps Oda found he really liked drawing rabbits like that. This would be very easy to write off if not for our second point of suspicion: Oda's oddly evasive response when it was brought up in an SBS.
Why did this person bring up the sea rabbits in this question if they weren't going to actually ask about them? Why did Oda let this question through? Why did Oda not address the sea rabbits as well? Why did Oda's response sound so taken aback, and why does he then rush to the next question? We can only speculate as to all of these, but the common consensus is that Oda wanted to bring attention to the scene without going into any detail, acting deliberately suspicious in his response so as to tip off the more attentive readers. It is also commonly assumed that the reason he would want to draw attention to it is because of its relation to Monet, who had supposedly died only a few chapters earlier and demonstrated a technique visually similar to these rabbits only shortly before that.
If these rabbits are related to her, though, the question is how. There have been numerous ideas over the years, but the ones I've seen the most often are as follows.

Perhaps it's just a coincidence, or perhaps Oda found he really liked drawing rabbits like that. This would be very easy to write off if not for our second point of suspicion: Oda's oddly evasive response when it was brought up in an SBS.
D: Regarding Chapter 700... Oops...! Good evening, Odacchi! Regarding Chapter 700, while Luffy and the others are on the way to Dressrosaroba, we can see animals that look like sea rabbits. What does Law like to eat other than Onigiri? P.N. Hasumomo
O: Well, ummm, grilled fish! Alright, next question.
Why did this person bring up the sea rabbits in this question if they weren't going to actually ask about them? Why did Oda let this question through? Why did Oda not address the sea rabbits as well? Why did Oda's response sound so taken aback, and why does he then rush to the next question? We can only speculate as to all of these, but the common consensus is that Oda wanted to bring attention to the scene without going into any detail, acting deliberately suspicious in his response so as to tip off the more attentive readers. It is also commonly assumed that the reason he would want to draw attention to it is because of its relation to Monet, who had supposedly died only a few chapters earlier and demonstrated a technique visually similar to these rabbits only shortly before that.
If these rabbits are related to her, though, the question is how. There have been numerous ideas over the years, but the ones I've seen the most often are as follows.
- Because Punk Hazard is the arc where Devil Fruit reincarnation was first introduced, this is symbolic of the Snow-Snow Fruit leaving Punk Hazard and finding purchase in one of Nami's tangerines. I personally disagree with this for two reasons: Nami takes good care of her tangerines and definitely would have found it by now, and the process of Devil Fruit reincarnation was shown to be instantaneous following Smiley's death. Even if there is a time delay to account for distance traveled, it probably still would have happened during the events of Punk Hazard, and not on the way to Dressrosa.
- They somehow indicate that Monet has boarded the Sunny, either symbolically or she literally boarded in that moment after riding atop or inside of the rabbits. This one I liked back during Dressrosa, but now that we're canonically about two months out from Punk Hazard, I find it pretty unlikely that she's been hiding on board this whole time, either because she would have made her move earlier or because she would have been found by now.
- It is purely symbolic of either Monet joining the crew, or of a rabbit (presumably Carrot) joining and gaining the Snow-Snow Fruit, represented by potentially literal snow rabbits surrounding the Straw Hats' ship. I generally dismiss this one on principal, just because I don't like to extrapolate meaning from symbolism, but rather from literal actions and dialogue. Others are free to make of this what they will, I just personally don't take it to mean that.
While Luffy, Law and the rest are in Caesar's cage and being put out into the open air to be exposed to Shinokuni, Chopper watches and readies himself to help, only to be interrupted by a flying, crumpled up note smacking him in the face, instructing him not to do anything and also seemingly providing him with notes on the drugs the children have been taking.
It's never explicitly stated who this note is from, and Monet clearly notices Chopper and doesn't immediately stop him. People have taken this to mean that Monet was somehow in on the plan, or that she figured the group might be able to help the children and didn't want to get in the way. Not to contradict my thesis by poking holes in evidence, but I personally think this point is completely wrong.
We know that Law can control things telekinetically with the Op-Op Fruit, so throwing a piece of paper definitely wouldn't be an issue. The main counterargument is that Law hadn't made a Room, so he couldn't have done it, but we know from the fight with Doflamingo that only the border of the Room is visible, so it's entirely possible that he had set one up much earlier, especially since he doesn't seem to activate a Room during the escape immediately following.
To counter this counterargument, though, Law has also shown the ability to send telepathic messages within a Room, or at least communicate discreetly, so it also may not necessarily make sense that he didn't just do that, although giving him the notes on the drugs probably would have been harder that way. It could pretty easily go either way.
Still, I think that Law being the one to do it makes the most sense, especially since Monet's actions through the rest of the arc strongly contradict the notion that she sent the note. I could turn out to be wrong, I just don't personally put any stock in this piece of evidence. Again, sorry to present contradictory evidence, but the best literature reviews acknowledge both sides of an argument rather than falling prey to confirmation bias. Remember that when you're doing college papers, kids.

It's never explicitly stated who this note is from, and Monet clearly notices Chopper and doesn't immediately stop him. People have taken this to mean that Monet was somehow in on the plan, or that she figured the group might be able to help the children and didn't want to get in the way. Not to contradict my thesis by poking holes in evidence, but I personally think this point is completely wrong.
We know that Law can control things telekinetically with the Op-Op Fruit, so throwing a piece of paper definitely wouldn't be an issue. The main counterargument is that Law hadn't made a Room, so he couldn't have done it, but we know from the fight with Doflamingo that only the border of the Room is visible, so it's entirely possible that he had set one up much earlier, especially since he doesn't seem to activate a Room during the escape immediately following.

To counter this counterargument, though, Law has also shown the ability to send telepathic messages within a Room, or at least communicate discreetly, so it also may not necessarily make sense that he didn't just do that, although giving him the notes on the drugs probably would have been harder that way. It could pretty easily go either way.

Still, I think that Law being the one to do it makes the most sense, especially since Monet's actions through the rest of the arc strongly contradict the notion that she sent the note. I could turn out to be wrong, I just don't personally put any stock in this piece of evidence. Again, sorry to present contradictory evidence, but the best literature reviews acknowledge both sides of an argument rather than falling prey to confirmation bias. Remember that when you're doing college papers, kids.
This one got a lot of people talking at the time, and actually prompted a bit of a resurgence in the Monet discourse. While showing off her collection of unusual creatures, Big Mom mentions that she recently retrieved a Centaur from Punk Hazard.
What "recent" means is up for debate. She's been dealing with Caesar for a few years, so maybe she got one of them when she sent an agent to check on Caesar's progress at some point, but it may also mean that one of her agents went to Punk Hazard while looking for Caesar after Luffy defeated him and picked up a Centaur at the time. Why one would still be there when all of them were arrested by G-5 is up for debate; maybe there was a straggler or an escapee? Either way, the theory of the day was that Big Mom's people had scoured the facility looking for Caesar or perhaps his research and in the meantime found Monet, bringing her back to Big Mom to put in her collection. I never really believed in this bit since I would think that a Harpy would be worth mentioning in the recent acquisitions, but even if there's a reason for Big Mom not mentioning Monet there, no Harpies were mentioned at any point during Whole Cake Island, and it doesn't seem too likely that we're going to revisit the collection, so I think this one's kind of past its expiration date. Even if Monet had escaped during the fire Jinbe set, it probably would have been noted, or at least there would have been an Easter egg that someone would have picked up on by now.
There is still hope, though, as it's possible this tidbit is meant to imply that the Big Mom Pirates did scour Punk Hazard, but didn't find Monet because she had already escaped. That does take a bit of a logical leap, but it seems odd to mention that Big Mom had collected a Centaur from Punk Hazard without anticipating it would bring Monet to mind. It's not particularly strong, but it revived the discussion for a time, so it's worth mentioning.

What "recent" means is up for debate. She's been dealing with Caesar for a few years, so maybe she got one of them when she sent an agent to check on Caesar's progress at some point, but it may also mean that one of her agents went to Punk Hazard while looking for Caesar after Luffy defeated him and picked up a Centaur at the time. Why one would still be there when all of them were arrested by G-5 is up for debate; maybe there was a straggler or an escapee? Either way, the theory of the day was that Big Mom's people had scoured the facility looking for Caesar or perhaps his research and in the meantime found Monet, bringing her back to Big Mom to put in her collection. I never really believed in this bit since I would think that a Harpy would be worth mentioning in the recent acquisitions, but even if there's a reason for Big Mom not mentioning Monet there, no Harpies were mentioned at any point during Whole Cake Island, and it doesn't seem too likely that we're going to revisit the collection, so I think this one's kind of past its expiration date. Even if Monet had escaped during the fire Jinbe set, it probably would have been noted, or at least there would have been an Easter egg that someone would have picked up on by now.
There is still hope, though, as it's possible this tidbit is meant to imply that the Big Mom Pirates did scour Punk Hazard, but didn't find Monet because she had already escaped. That does take a bit of a logical leap, but it seems odd to mention that Big Mom had collected a Centaur from Punk Hazard without anticipating it would bring Monet to mind. It's not particularly strong, but it revived the discussion for a time, so it's worth mentioning.
I'll preface this by saying I do not put stock into cover page theories. Nekomamushi's 13 cats, Sanji's suitcase labeled "The Secret," Zoro's shirt of death, I don't trust any of them, and this one is no exception, but it seemed to have quite a bit of traction back in the day, so I would be remiss not to at least call attention to it.
Note the two prominent snowmen that the crew are building. One is a larger male, while the other is a thin woman with wavy hair. The conceit of the theory was that this image was meant to show the final lineup of the crew. At the time, we already knew that Jinbe was planning to join the crew, so people took the larger male wearing the Straw Hat to represent Jinbe, and the female, a woman made of snow with hair styled similarly to Monet, to represent Monet. I believe some people also attributed the giant snowman in the back to the idea that a Giant was going to join, but I may be misremembering that, I apologize. Either way, the only part of this that I think holds any water is the hairstyle, but I honestly just don't think that this means anything. The only way I could at this point is if Monet is the next to join and then we get a giant, but I think we all already know my thoughts on the final lineup (just keep reading if you don't), and this just doesn't match. I could be wrong, there's plenty of time for the story to go any way and this may be a blueprint for how it will go, I just don't ascribe to this theory in particular.

Note the two prominent snowmen that the crew are building. One is a larger male, while the other is a thin woman with wavy hair. The conceit of the theory was that this image was meant to show the final lineup of the crew. At the time, we already knew that Jinbe was planning to join the crew, so people took the larger male wearing the Straw Hat to represent Jinbe, and the female, a woman made of snow with hair styled similarly to Monet, to represent Monet. I believe some people also attributed the giant snowman in the back to the idea that a Giant was going to join, but I may be misremembering that, I apologize. Either way, the only part of this that I think holds any water is the hairstyle, but I honestly just don't think that this means anything. The only way I could at this point is if Monet is the next to join and then we get a giant, but I think we all already know my thoughts on the final lineup (just keep reading if you don't), and this just doesn't match. I could be wrong, there's plenty of time for the story to go any way and this may be a blueprint for how it will go, I just don't ascribe to this theory in particular.
I know I said I'd be going greatest to least, but I didn't really want to end this on such a weak note, and these patterns may end up applying to someone else anyway, so while I think they help support Monet's return and recruitment, you may feel that they're completely unrelated or irrelevant. I'm also counting these all as one point because I feel that it's only when the patterns are taken in aggregate that they become a decent argument for Monet's inclusion, as any given one of these patterns could easily be debunked at any time.
The most obvious pattern is that she's a female villain, and as I mentioned earlier, this was likely the biggest contributing factor for fans to start keeping their eyes on her. It certainly didn't hurt that she was introduced right after Jinbe was invited to join the crew, which would make her the second recruit of the New World, fitting in with the MFMM Pattern. To summarize, each sea comes with four recruits, a male, a female, and two more males, so with Jinbe confirming his interest in joining the crew, he obviously took the first M, opening the door for the New World's F. I've talked about my thoughts on this pattern before, and while I think that there is more to the pattern that will allow other females to join the crew as well (specifically Pudding and Carrot), right now we're just talking about Monet, so MFMM works fine.
A secondary aspect of the MFMM pattern, which not everyone seems to ascribe to but is still fairly common, is the characteristics of the recruits. Zoro, Chopper and Jinbe are all considered monsters by the public, Nami and Robin are anti-villains, Usopp and Franky are members of troublemaking groups and were recruited in arcs where the crew got a new ship, and Sanji and Brook are perverted gentlemen. Even if we disregard the MFMM pattern in its current form, we can still potentially apply Monet to any of the remaining three archetypes. Obviously she's a villain, but if the theory that she wants to protect the children without compromising her mission is true, that would clearly establish her as an anti-villain. She was a member of the Donquixote Pirates, the most extreme level of troublemaker I can think of, though it's possible her backstory will provide a better example, and if she does in fact end up being related to the crew going to the moon, she'd likely be recruited around the time they get the means to make such a journey. As for being a perverted gentleman, she doesn't quite fit the bill, but we do know that she worked as a maid for the royal family of Dressrosa, implying she has the etiquette of a lady, and she has been shown to be flirtatious, yet shy when being flirted with. Therefore, in place of a perverted gentleman, I think we can label her a flirtatious lady, fitting the same general archetype just with different terms.
Honestly, "perverted gentleman" is a label the fans came up with. "Polite flirts" gets across the exact same idea without assuming gender, so honestly it works just fine. You could even just label them as "hopeless romantics" if you want. Not to mention the fact that it'd just be interesting to see a female character objectifying male characters for once, or even to have someone be actively flattered by Sanji and Brook's behavior instead of just getting into a fight. It's nice to think that the final recruits will provide new spins on the established formula instead of just falling in line with it.
A less obvious, but fairly popular pattern to apply to Monet is the 325 Pattern, in which the pronunciation of each of the Devil Fruit within the Straw Hat Crew can be read as a number through goroawase, Japanese wordplay. Gomu=5 and 6, Hito= 1 and 10, Hana= 8 and 7, Yomi= 4 and 3. Taken as single numbers and adding them together, we are left with 296. If we assume that there will be no repeats in future Devil Fruit using recruits, then we are left with 0, 2 and 9. Taken as 20+9 or 0+29, we can add those to our 296 and get 325, which in goroawase would be pronounced Sa-Ni-Go, or Sunny-Go, 'Go' being a common suffix used when referring to ships in Japanese. Some people ignore the 0 because it isn't necessary to reach 325, meaning we only need a 29. If we assume that to be true, you could get Kuma's Nikyu-Nikyu Fruit or Kinemon's Fuku-Fuku Fruit, as 2 can be either ni or fu, and 9 can be ku or kyu. I personally think that's too obvious, though, and given the narrative of both of those characters, I'm not inclined to see either of them happening. No, I think Oda would want to hide who the remaining two are, and while I'll cover my thoughts on the 20 later, the 9 has been hiding in plain sight this entire time. Monet's Yuki-Yuki Fruit, obviously contains yu and ki. On their own, they aren't generally read as any numbers, but if you reverse them, you get ki-yu. When 9 is read as kyu, it's specifically a contraction of ki and yu. In other words, Yuki can be seen as 9 backwards. That said, this is a good time to mention that another of my top picks, Pudding, has the Memo-Memo Fruit, which as near as I can find does not fit any number wordplay, so there's definitely room for this pattern to be debunked wholesale, but if it's true, Monet still has a fair chance of fitting it.
Speaking of goroawase, an offshoot of the MFMM Pattern is the Straw Hat 13 Pattern, in which the word for crew, ichimi, can be read as 1 and 3, which people take to mean there will be a total of 13 members in the crew. This doesn't pertain too much to Monet in and of itself, but the Straw Hat 13 is often backed up by the Alphabet Pattern, in which the first letter of each Straw Hat's name uses a letter from one of thirteen pairs of letters in the Latin alphabet without any overlap (AB=Brook, CD=Chopper, EF=Franky, JI=Jinbe, KL=Luffy, MN=Nami, QR=Robin, ST=Sanji, UV=Usopp, YZ=Zoro, with GH, OP and WX so far unused). People generally use this one to debunk Monet, as she would be MN, but in much the same way I think Oda is trying to hide the goroawase hint, so too do I think he's hiding how the remaining recruits fit the Alphabet Pattern. In Monet's case, if Monet's epithet is revealed to be Harpy she would fit GH. Even if that doesn't work, keep in mind what I said earlier: everyone in the Donquixote Pirates used codenames, and we still don't know Monet's real name. Her real name could easily land her in any of the remaining pairs, but as I've said in previous theories, I think she'll end up with GH, and that OP and WX will go to Pudding and Carrot, with Carrot receiving WX along with an epithet she is assigned after being confirmed as a Straw Hat (likely including 'White' for her fur). Honestly I wouldn't be too surprised if it turned out her name was Happy like she has written across her tanktop and the pun was just a distraction.
Another fan favorite, and one that I think people tend to prioritize above most others due to being based on Oda's own words, is the Color Pattern. Oda has explicitly stated that each of the Straw Hats has a signature color associated with them, and while those colors aren't always incorporated into their palettes, they do tend to be referenced in things such as color pages. Luffy=red, Nami=orange, Usopp=yellow, Zoro=green, Franky=light blue, Sanji=blue, Robin=purple, Chopper=pink, and Brook=black and white, while Jinbe has yet to be assigned a color, though I imagine it's forthcoming. The common method for predicting future Straw Hats based on this pattern is to look at what colors haven't been used yet. Strictly speaking, there are infinite colors that haven't been used, so to narrow it down, people generally look to tertiary color wheels, in which there are twelve colors excluding black and white. I don't want to turn this into a theory on the matter, so to summarize: using the official RBY (red-blue-yellow) color wheel, the colors don't actually line up with the crew because it doesn't officially have pink, rather the much deeper magenta, excluding Chopper; the RGB (red-green-blue) wheel, on the other hand fits everyone, though with different official terms, and still leaves room for others.
In this case, both rose and magenta fit pink much better than the deep magenta of RBY, with cyan being an alternate name for Franky's light blue and violet for Robin's purple. With the remaining colors, chartreuse, spring green (aka viridian) and magenta (I'm assuming rose is meant to be pink), we can easily fit Monet on either side of Zoro, though I'm inclined to label her as chartreuse myself. Incidentally, many of Pudding's outfits see her on the redder side of the spectrum, potentially allowing her to take the magenta spot, while several of Carrot's outfits include elements of green that closely match viridian. Again, though, we're here to talk about Monet, and she fits regardless of their color schemes. I'd also like to point out that considering Monet as just another shade of green puts her in an interesting trio with Nami and Robin, as all three of them would be secondary colors. Doesn't necessarily mean anything, but man would that give the three of them a nice aesthetic.
If there is a theory that people believe in more than the Color Pattern, though, it would have to be Usopp's lies coming true (or Usopp's True Lies, as I call them). As Usopp's lies have a tendency to come true, people have been waiting with bated breath for his lie from Thriller Bark to come true. For those who don't recall, after Luffy, Zoro and Sanji have their shadows stolen by Gecko Moria and are forecast to be catatonic for the next three days, Usopp declares that a beautiful swordswoman has arrived carrying meat, appealing to all three of their unique sensibilities and forcing them to awaken. People generally use this as justification for Tashigi to join, as she is a beautiful swordswoman, and anticipate that when she joins she will bring meat as a peace offering for Luffy. They also applied this logic to Rebecca for a while, as she also fit the bill and bought food for Luffy when he was hungry. The jury is still out on her joining, but it's not looking particularly likely right now given her character arc's focus on pacifism. Once Rebecca stopped seeming like such a viable candidate, people started to shift their focus to the upcoming Wano arc and assumed that either a kunoichi or female samurai would join the crew. As of yet, though, none of the characters in the arc have matched that description either. Tama, the kunoichi in training, gave Luffy rice, not meat, and doesn't have a sword. Shinobu, the professional kunoichi, has a sword, but hasn't really been shown using it so much as she uses thrown weapons, and she hasn't given the crew any food to speak of. Kikunojo, a beautiful samurai, similarly has not presented meat to the crew, and is also one of the Nine Red Scabbards, who I don't see leaving any of their ranks with the Straw Hats, personally. The last likely candidate would be Hiyori, who is universally considered beautiful in canon and grants Zoro the Ame no Habakiri sword, and after the battle at Onigashima, it's entirely possible that she'll have a banquet waiting for the surviving warriors, but I honestly see her somehow getting dragged into the conflict (probably by Kanjuro), and even afterwards staying at Wano to rule while Momo joins the crew.
But what does this have to do with Monet? She's not a swordswoman, and she definitely hasn't given Luffy any meat. Well, if we're willing to postpone the presenting of meat for Tashigi and anyone from Wano, there's no reason we can't do the same for Monet. As for being a swordswoman, you're right, she isn't, at least not in the traditional sense. As with other patterns, her eligibility for this pattern may be obscured, as she actually has two ways of qualifying: her signature over-sized ice picks, and her ability to freeze her feathers to use her wings as blades, an attack explicitly referred to as "Skin Katana" for some reason.
A normal ice pick definitely wouldn't qualify as a sword, but at the size that Monet uses them, they function essentially the same as a rapier or an epee or any other non-edged swords, focusing primarily on thrusts but still capable of slashing with the tip. Her wings are a little harder to justify, as just having the word "katana" in the attack name doesn't actually make it a sword, but their function as a bladed melee weapon remains. No matter which one you look at, though, she actually becomes eligible for filling a role that many fans have been suggesting for some time: a dual sword user. When Kinemon was first introduced, people thought for sure the two swords at his side meant that he would form a "Musketeer Trio" with Zoro's three swords and Brook's one, but Monet's two picks or two wings both seem like they could easily count. People might complain that having two sword users that use ice would be redundant, but we already went over that concept in point 8, so I won't talk about it again. I don't think Monet necessarily would be in that trio, though, I just think it's interesting to consider. There's also the fact that since she has the picks and her wings, she'd technically be a four-sword user like Kaku, but she's never shown using them at the same time, so she's only two swords at a time.
Adding on to her fighting capabilities, many people believe that the Straw Hats are destined to get a Logia user on the crew, as that is the only Devil Fruit type not yet represented. We already have three Paramecia (Luffy, Robin and Brook) and one or two Zoans (Chopper and Momo if you count him), so having one Logia would complete the package. The number of each may be irrelevant though, especially since whether Momo counts is dubious and Pudding, another Paramecia, may or may not join. There's also the fact that many people believe that either Smoker or Crocodile will join as the crew's Logia, but I don't personally think that either of them will, and even if they do, that doesn't mean that Monet won't join.
Beyond all of these patterns that have been floating around the theorist community for several years, I've noticed four of my own that I'd never heard anyone else discuss. Again, I've talked about these in the past, so I'll just summarize them here. Like Nami and Robin, Monet has been shown to have had short hair (neck to shoulder length) pre-timeskip and now has long hair (mid to lower back) post-timeskip.
A few other characters fit this pattern as well, so this isn't exactly a clincher, but it certainly doesn't hurt her chances.
Nami and Robin also both lead Luffy into a trap by tricking him (Nami pretending to team up with him, Robin with a sign), wherein he is put into a cage and awaits death from the arc villain (Buggy's Buggy Ball cannon, Crocodile's lair filling with water). Monet doesn't trick Luffy, and is only tangentially responsible for his capture since she reported his presence to Caesar, but he does still end up in a cage and waiting for death (the spread of Caesar's Shinokuni).
As a bit of a bonus, Robin even points out how similar this situation is to the one in Alabasta, making it seem that the parallel is intentional, so even if it's not perfect, it may still count. Admittedly, Pudding fits this one better, as she's the only other character I've found that's tricked Luffy into a cage, but a weak parallel is a parallel nonetheless.
Going back to the argument that Monet's been gone too long to be relevant, I would like to remind everyone that Robin didn't join the crew until the fourth arc after her introduction (Whiskey Peak [1], Little Garden [2], Drum Island [3], Alabasta [4]), and only played a particularly big role in the latter of those four. Nami, similarly, only began identifying as a member of the crew in her fourth arc, as she had always planned to betray the crew up through the first three (Orange Town, Syrup Village, Baratie, Arlong Park). For Monet, it's definitely been too many arcs since Punk Hazard, but it hasn't been too many sagas. In fact, there is precedent for a four-saga delay, as Jinbe was asked to join the crew during the Fishman Island Saga, was absent through Dressrosa, proclaimed his intent to join at Whole Cake Island, and then actually joined during Wano. Since Whole Cake and Wano are both technically in the Yonko Saga, you could also look at it from Jinbe's introduction during the Summit War Saga, going to Fishman Island, Dressrosa, and then the Yonko Saga. Depending on which logic you use, Monet's return could be as early as the next saga (Dressrosa, Whole Cake, Wano, ???) or the saga that's two out (Dressrosa, Yonko, ??? 1, ??? 2). I'm not saying this is a hard time limit for her to come back, but that's a decent chunk of time and who knows how many smaller arcs within, so I'd be pretty surprised if it takes longer than that.
Of the four patterns I found, Monet's strongest comes from her introduction. Monet's introductory panel, the one in which her name card is formally presented to the audience, sees her taking a similar pose to that which Nami and Robin took in their introductions, being that she is sitting atop an elevated platform with her legs dangling over the edge while looking down at Luffy, though in Monet's case she's looking at his picture in a newspaper rather than the genuine article.
As far as I could find, Monet is the only character whose name card scene so closely mirrors theirs, though other characters (Marguerite and Carrot) are formally introduced to Luffy from similar positions, just outside of their name card scenes. Monet's definitely has the strongest resemblance though, at least in my opinion.
And with that, I think we've covered all of the most key points of the Monet Theory literature. You are free to believe or disbelieve whichever combination you want, lord knows I don't believe all of them, but taken in aggregate, it isn't hard to see why people have been willing to stand behind Monet for so long. As I said earlier, if I somehow missed anything, please, let me know.
The most obvious pattern is that she's a female villain, and as I mentioned earlier, this was likely the biggest contributing factor for fans to start keeping their eyes on her. It certainly didn't hurt that she was introduced right after Jinbe was invited to join the crew, which would make her the second recruit of the New World, fitting in with the MFMM Pattern. To summarize, each sea comes with four recruits, a male, a female, and two more males, so with Jinbe confirming his interest in joining the crew, he obviously took the first M, opening the door for the New World's F. I've talked about my thoughts on this pattern before, and while I think that there is more to the pattern that will allow other females to join the crew as well (specifically Pudding and Carrot), right now we're just talking about Monet, so MFMM works fine.
A secondary aspect of the MFMM pattern, which not everyone seems to ascribe to but is still fairly common, is the characteristics of the recruits. Zoro, Chopper and Jinbe are all considered monsters by the public, Nami and Robin are anti-villains, Usopp and Franky are members of troublemaking groups and were recruited in arcs where the crew got a new ship, and Sanji and Brook are perverted gentlemen. Even if we disregard the MFMM pattern in its current form, we can still potentially apply Monet to any of the remaining three archetypes. Obviously she's a villain, but if the theory that she wants to protect the children without compromising her mission is true, that would clearly establish her as an anti-villain. She was a member of the Donquixote Pirates, the most extreme level of troublemaker I can think of, though it's possible her backstory will provide a better example, and if she does in fact end up being related to the crew going to the moon, she'd likely be recruited around the time they get the means to make such a journey. As for being a perverted gentleman, she doesn't quite fit the bill, but we do know that she worked as a maid for the royal family of Dressrosa, implying she has the etiquette of a lady, and she has been shown to be flirtatious, yet shy when being flirted with. Therefore, in place of a perverted gentleman, I think we can label her a flirtatious lady, fitting the same general archetype just with different terms.

Honestly, "perverted gentleman" is a label the fans came up with. "Polite flirts" gets across the exact same idea without assuming gender, so honestly it works just fine. You could even just label them as "hopeless romantics" if you want. Not to mention the fact that it'd just be interesting to see a female character objectifying male characters for once, or even to have someone be actively flattered by Sanji and Brook's behavior instead of just getting into a fight. It's nice to think that the final recruits will provide new spins on the established formula instead of just falling in line with it.
A less obvious, but fairly popular pattern to apply to Monet is the 325 Pattern, in which the pronunciation of each of the Devil Fruit within the Straw Hat Crew can be read as a number through goroawase, Japanese wordplay. Gomu=5 and 6, Hito= 1 and 10, Hana= 8 and 7, Yomi= 4 and 3. Taken as single numbers and adding them together, we are left with 296. If we assume that there will be no repeats in future Devil Fruit using recruits, then we are left with 0, 2 and 9. Taken as 20+9 or 0+29, we can add those to our 296 and get 325, which in goroawase would be pronounced Sa-Ni-Go, or Sunny-Go, 'Go' being a common suffix used when referring to ships in Japanese. Some people ignore the 0 because it isn't necessary to reach 325, meaning we only need a 29. If we assume that to be true, you could get Kuma's Nikyu-Nikyu Fruit or Kinemon's Fuku-Fuku Fruit, as 2 can be either ni or fu, and 9 can be ku or kyu. I personally think that's too obvious, though, and given the narrative of both of those characters, I'm not inclined to see either of them happening. No, I think Oda would want to hide who the remaining two are, and while I'll cover my thoughts on the 20 later, the 9 has been hiding in plain sight this entire time. Monet's Yuki-Yuki Fruit, obviously contains yu and ki. On their own, they aren't generally read as any numbers, but if you reverse them, you get ki-yu. When 9 is read as kyu, it's specifically a contraction of ki and yu. In other words, Yuki can be seen as 9 backwards. That said, this is a good time to mention that another of my top picks, Pudding, has the Memo-Memo Fruit, which as near as I can find does not fit any number wordplay, so there's definitely room for this pattern to be debunked wholesale, but if it's true, Monet still has a fair chance of fitting it.
Speaking of goroawase, an offshoot of the MFMM Pattern is the Straw Hat 13 Pattern, in which the word for crew, ichimi, can be read as 1 and 3, which people take to mean there will be a total of 13 members in the crew. This doesn't pertain too much to Monet in and of itself, but the Straw Hat 13 is often backed up by the Alphabet Pattern, in which the first letter of each Straw Hat's name uses a letter from one of thirteen pairs of letters in the Latin alphabet without any overlap (AB=Brook, CD=Chopper, EF=Franky, JI=Jinbe, KL=Luffy, MN=Nami, QR=Robin, ST=Sanji, UV=Usopp, YZ=Zoro, with GH, OP and WX so far unused). People generally use this one to debunk Monet, as she would be MN, but in much the same way I think Oda is trying to hide the goroawase hint, so too do I think he's hiding how the remaining recruits fit the Alphabet Pattern. In Monet's case, if Monet's epithet is revealed to be Harpy she would fit GH. Even if that doesn't work, keep in mind what I said earlier: everyone in the Donquixote Pirates used codenames, and we still don't know Monet's real name. Her real name could easily land her in any of the remaining pairs, but as I've said in previous theories, I think she'll end up with GH, and that OP and WX will go to Pudding and Carrot, with Carrot receiving WX along with an epithet she is assigned after being confirmed as a Straw Hat (likely including 'White' for her fur). Honestly I wouldn't be too surprised if it turned out her name was Happy like she has written across her tanktop and the pun was just a distraction.
Another fan favorite, and one that I think people tend to prioritize above most others due to being based on Oda's own words, is the Color Pattern. Oda has explicitly stated that each of the Straw Hats has a signature color associated with them, and while those colors aren't always incorporated into their palettes, they do tend to be referenced in things such as color pages. Luffy=red, Nami=orange, Usopp=yellow, Zoro=green, Franky=light blue, Sanji=blue, Robin=purple, Chopper=pink, and Brook=black and white, while Jinbe has yet to be assigned a color, though I imagine it's forthcoming. The common method for predicting future Straw Hats based on this pattern is to look at what colors haven't been used yet. Strictly speaking, there are infinite colors that haven't been used, so to narrow it down, people generally look to tertiary color wheels, in which there are twelve colors excluding black and white. I don't want to turn this into a theory on the matter, so to summarize: using the official RBY (red-blue-yellow) color wheel, the colors don't actually line up with the crew because it doesn't officially have pink, rather the much deeper magenta, excluding Chopper; the RGB (red-green-blue) wheel, on the other hand fits everyone, though with different official terms, and still leaves room for others.

In this case, both rose and magenta fit pink much better than the deep magenta of RBY, with cyan being an alternate name for Franky's light blue and violet for Robin's purple. With the remaining colors, chartreuse, spring green (aka viridian) and magenta (I'm assuming rose is meant to be pink), we can easily fit Monet on either side of Zoro, though I'm inclined to label her as chartreuse myself. Incidentally, many of Pudding's outfits see her on the redder side of the spectrum, potentially allowing her to take the magenta spot, while several of Carrot's outfits include elements of green that closely match viridian. Again, though, we're here to talk about Monet, and she fits regardless of their color schemes. I'd also like to point out that considering Monet as just another shade of green puts her in an interesting trio with Nami and Robin, as all three of them would be secondary colors. Doesn't necessarily mean anything, but man would that give the three of them a nice aesthetic.
If there is a theory that people believe in more than the Color Pattern, though, it would have to be Usopp's lies coming true (or Usopp's True Lies, as I call them). As Usopp's lies have a tendency to come true, people have been waiting with bated breath for his lie from Thriller Bark to come true. For those who don't recall, after Luffy, Zoro and Sanji have their shadows stolen by Gecko Moria and are forecast to be catatonic for the next three days, Usopp declares that a beautiful swordswoman has arrived carrying meat, appealing to all three of their unique sensibilities and forcing them to awaken. People generally use this as justification for Tashigi to join, as she is a beautiful swordswoman, and anticipate that when she joins she will bring meat as a peace offering for Luffy. They also applied this logic to Rebecca for a while, as she also fit the bill and bought food for Luffy when he was hungry. The jury is still out on her joining, but it's not looking particularly likely right now given her character arc's focus on pacifism. Once Rebecca stopped seeming like such a viable candidate, people started to shift their focus to the upcoming Wano arc and assumed that either a kunoichi or female samurai would join the crew. As of yet, though, none of the characters in the arc have matched that description either. Tama, the kunoichi in training, gave Luffy rice, not meat, and doesn't have a sword. Shinobu, the professional kunoichi, has a sword, but hasn't really been shown using it so much as she uses thrown weapons, and she hasn't given the crew any food to speak of. Kikunojo, a beautiful samurai, similarly has not presented meat to the crew, and is also one of the Nine Red Scabbards, who I don't see leaving any of their ranks with the Straw Hats, personally. The last likely candidate would be Hiyori, who is universally considered beautiful in canon and grants Zoro the Ame no Habakiri sword, and after the battle at Onigashima, it's entirely possible that she'll have a banquet waiting for the surviving warriors, but I honestly see her somehow getting dragged into the conflict (probably by Kanjuro), and even afterwards staying at Wano to rule while Momo joins the crew.
But what does this have to do with Monet? She's not a swordswoman, and she definitely hasn't given Luffy any meat. Well, if we're willing to postpone the presenting of meat for Tashigi and anyone from Wano, there's no reason we can't do the same for Monet. As for being a swordswoman, you're right, she isn't, at least not in the traditional sense. As with other patterns, her eligibility for this pattern may be obscured, as she actually has two ways of qualifying: her signature over-sized ice picks, and her ability to freeze her feathers to use her wings as blades, an attack explicitly referred to as "Skin Katana" for some reason.

A normal ice pick definitely wouldn't qualify as a sword, but at the size that Monet uses them, they function essentially the same as a rapier or an epee or any other non-edged swords, focusing primarily on thrusts but still capable of slashing with the tip. Her wings are a little harder to justify, as just having the word "katana" in the attack name doesn't actually make it a sword, but their function as a bladed melee weapon remains. No matter which one you look at, though, she actually becomes eligible for filling a role that many fans have been suggesting for some time: a dual sword user. When Kinemon was first introduced, people thought for sure the two swords at his side meant that he would form a "Musketeer Trio" with Zoro's three swords and Brook's one, but Monet's two picks or two wings both seem like they could easily count. People might complain that having two sword users that use ice would be redundant, but we already went over that concept in point 8, so I won't talk about it again. I don't think Monet necessarily would be in that trio, though, I just think it's interesting to consider. There's also the fact that since she has the picks and her wings, she'd technically be a four-sword user like Kaku, but she's never shown using them at the same time, so she's only two swords at a time.
Adding on to her fighting capabilities, many people believe that the Straw Hats are destined to get a Logia user on the crew, as that is the only Devil Fruit type not yet represented. We already have three Paramecia (Luffy, Robin and Brook) and one or two Zoans (Chopper and Momo if you count him), so having one Logia would complete the package. The number of each may be irrelevant though, especially since whether Momo counts is dubious and Pudding, another Paramecia, may or may not join. There's also the fact that many people believe that either Smoker or Crocodile will join as the crew's Logia, but I don't personally think that either of them will, and even if they do, that doesn't mean that Monet won't join.
Beyond all of these patterns that have been floating around the theorist community for several years, I've noticed four of my own that I'd never heard anyone else discuss. Again, I've talked about these in the past, so I'll just summarize them here. Like Nami and Robin, Monet has been shown to have had short hair (neck to shoulder length) pre-timeskip and now has long hair (mid to lower back) post-timeskip.

A few other characters fit this pattern as well, so this isn't exactly a clincher, but it certainly doesn't hurt her chances.
Nami and Robin also both lead Luffy into a trap by tricking him (Nami pretending to team up with him, Robin with a sign), wherein he is put into a cage and awaits death from the arc villain (Buggy's Buggy Ball cannon, Crocodile's lair filling with water). Monet doesn't trick Luffy, and is only tangentially responsible for his capture since she reported his presence to Caesar, but he does still end up in a cage and waiting for death (the spread of Caesar's Shinokuni).

As a bit of a bonus, Robin even points out how similar this situation is to the one in Alabasta, making it seem that the parallel is intentional, so even if it's not perfect, it may still count. Admittedly, Pudding fits this one better, as she's the only other character I've found that's tricked Luffy into a cage, but a weak parallel is a parallel nonetheless.
Going back to the argument that Monet's been gone too long to be relevant, I would like to remind everyone that Robin didn't join the crew until the fourth arc after her introduction (Whiskey Peak [1], Little Garden [2], Drum Island [3], Alabasta [4]), and only played a particularly big role in the latter of those four. Nami, similarly, only began identifying as a member of the crew in her fourth arc, as she had always planned to betray the crew up through the first three (Orange Town, Syrup Village, Baratie, Arlong Park). For Monet, it's definitely been too many arcs since Punk Hazard, but it hasn't been too many sagas. In fact, there is precedent for a four-saga delay, as Jinbe was asked to join the crew during the Fishman Island Saga, was absent through Dressrosa, proclaimed his intent to join at Whole Cake Island, and then actually joined during Wano. Since Whole Cake and Wano are both technically in the Yonko Saga, you could also look at it from Jinbe's introduction during the Summit War Saga, going to Fishman Island, Dressrosa, and then the Yonko Saga. Depending on which logic you use, Monet's return could be as early as the next saga (Dressrosa, Whole Cake, Wano, ???) or the saga that's two out (Dressrosa, Yonko, ??? 1, ??? 2). I'm not saying this is a hard time limit for her to come back, but that's a decent chunk of time and who knows how many smaller arcs within, so I'd be pretty surprised if it takes longer than that.
Of the four patterns I found, Monet's strongest comes from her introduction. Monet's introductory panel, the one in which her name card is formally presented to the audience, sees her taking a similar pose to that which Nami and Robin took in their introductions, being that she is sitting atop an elevated platform with her legs dangling over the edge while looking down at Luffy, though in Monet's case she's looking at his picture in a newspaper rather than the genuine article.

As far as I could find, Monet is the only character whose name card scene so closely mirrors theirs, though other characters (Marguerite and Carrot) are formally introduced to Luffy from similar positions, just outside of their name card scenes. Monet's definitely has the strongest resemblance though, at least in my opinion.
And with that, I think we've covered all of the most key points of the Monet Theory literature. You are free to believe or disbelieve whichever combination you want, lord knows I don't believe all of them, but taken in aggregate, it isn't hard to see why people have been willing to stand behind Monet for so long. As I said earlier, if I somehow missed anything, please, let me know.
Now, before we move on to the predictions, let's review: People believe that Monet is alive and will join the crew for a fairly sizable list of reasons, though some are stronger or weaker than others.
Man, this has already shaped up to be my longest theory ever (Oro Jackson included) and I haven't even made one prediction yet!
- Her heart was shown to be intact, and the shrapnel Caesar tried to stab it with was embedded into the dock next to it, implying that Caesar's hand slipped as he stabbed at it and he fell unconscious before he could try again. This is the strongest piece of evidence, as it eliminates the one reason to believe that Monet is dead and suggests that Oda has more planned for Monet as a character.
- Monet's backstory and relationships are left fairly vague, only being discussed in any detail in an SBS. Her sibling relationship to Sugar is never acknowledged in series, and her belief that Doflamingo will become Pirate King seems to be completely unfounded as even he never shows any desire to do so. Less relevant characters have received more indepth backstories both in the series proper and in the SBS, so for Monet's to be so vague but still have elements left open to explore gives the impression that Oda intends to do so.
- Her interest in astronomy, as demonstrated by her various textbooks with titles seemingly related to the subject, is fairly unique, and again, never focused on. It doesn't even come up in the SBS or in databooks, so it seems odd not to give it any attention. Furthermore, because of Enel's story on the moon where he found aliens and a connection between the moon and the Sky People, it is widely believed that there will come a time that the Straw Hats go to the moon, so the only character to ever show interest in astronomy would be a logical companion for said arc.
- Monet's tattoo is only shown once and obscured, not even appearing in several other panels where it should be completely visible. The fact that this tattoo exists but both Oda and Monet have clearly gone to great lengths to hide it strongly implies that there is significance to it and that Monet is in some way motivated not to let other people see it.
- The wings and other bird parts that Monet has Law graft onto her seem like much too drastic of a change for a perfectly healthy woman to decide to commit to on a whim, so it stands to reason that it was likely important to her to make that replacement. It may have something to do with the tattoo, as one of her wings did completely replace the arm where the tattoo once was, and the two may be intertwined in her backstory.
- Brownbeard and his subordinates formed a search team to scour Punk Hazard for the victims of Caesar's Shinokuni, putting them in a good position to potentially find Monet, return her heart, and arrest her. This could bring Monet back to the story with her breaking out of prison, but we also know that she was in a sealed room, so it's possible that Oda deliberately had them miss her so she could leave Punk Hazard on her own.
- Monet's personality at first seems to be completely built on sadism and pragmatism, but she consistently shows concern for the subordinates that Caesar abandons, and was even the one to suggest that Law make the paraplegic victims of Caesar's gas weapon into centaurs despite the fact that they were already loyal and given the means to move about independently. Moreover, despite the fact that she was complicit in Caesar's experimentation on the children, Monet's dialogue and actions suggest that she did actually care for them, as she was assigned to "protect Caesar's experiments" by Doflamingo, but instead of protecting the SAD that Doflamingo actually cares about, she chose to protect the children. Even after learning the truth about Caesar, the children still trusted Monet because of how kindly she had treated them. Altogether, it's perfectly conceivable that Monet had to choose between protecting the children and protecting herself from/staying loyal to Doflamingo, and thus chose to make sure the children did not suffer so long as they were under Caesar's control.
- Luffy's love of snow was the first tip-off for many readers that Monet may join the crew, as Luffy consistently expresses that he wants to go to snow islands, and as has been shown time and again, what Luffy wants, Luffy gets.
- A horde of sea rabbits are seen beneath the waves while the crew is on the way to Punk Hazard, but are never acknowledged in story and are referred to dismissively and suspiciously in an SBS. Their uncanny resemblance to one of Monet's attacks, Snow Rabbits, has suggested to many fans that they may be a snow construct made by Monet for some reason, were a symbol of Monet's Devil Fruit finding purchase in one of Nami's tangerines to be eaten by someone else later, or were symbolic foreshadowing of either a rabbit or Monet joining the Straw Hat Crew. This is one of the weaker pieces of evidence, but it's not impossible for it to still turn out to be relevant later.
- The note thrown to Chopper while Luffy and Law were in Caesar's cage seems unlikely to many fans to have been thrown by Law, as there was no indication that he had a Room already set up, so it was once a popular theory that Monet threw the note. However, Law was seen using his ability moments later, still not setting up a Room, suggesting he just had one up that was too big to see the borders of at the moment. Furthermore, Monet's actions through the rest of the arc contradict any motivation she would have to help the crew, so unless she's a very committed actor, this one is not particularly likely.
- Big Mom's collection of strange creatures includes a centaur from Punk Hazard as a recent edition, implying that the Big Mom Pirates picked one up either on a recent visit to Punk Hazard to deliver supplies to Caesar or when they went after the events of the Punk Hazard Arc to retrieve him from the Straw Hats. If they had gone to Punk Hazard at that juncture, it wouldn't be odd for them to also find Monet and add her to the collection. However, Big Mom likely would have mentioned her as one of her recent acquisitions, and it doesn't seem particularly likely that we'll be revisiting the concept of her collection any time soon, so it's unlikely that Monet is there.
- One color spread depicted the Straw Hats building three snowmen, one quite large and round, one clearly a woman with a relatively slender figure and similar hair to Monet, and a giant one peeking in from the background. It has been suggested that this cover is meant to foreshadow the crew's final roster, with the large male representing Jinbe, the woman representing Monet, and the giant representing a Giant, the latter being a fairly popular theory. I, however, do not put stock in cover-based theories, nor do I believe that a Giant will join the crew proper, so I personally discount this one entirely, but others are free to make of it what they will.
- Monet fits several miscellaneous patterns that theorists have suggested over the years, including the delay between her introduction and her potential recruitment, her main color being a green distinct from Zoro's, her hairstyles pre- and post-timeskip being similar to Nami and Robin's, her introductory panel sharing visual elements with Nami and Robin's, her real name potentially starting with a letter not already represented in the Straw Hat's names, her Devil Fruit's name being readable as the Japanese word for "nine" backwards to fit with the readings of the other Straw Hat Fruit, and a number of others.
Man, this has already shaped up to be my longest theory ever (Oro Jackson included) and I haven't even made one prediction yet!
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