JUDAS CONTRACT
Here's another big one.
Some have already pointed out that Kanjuro's potential treason may ultimately be grounded in the tale of an infamous real life historical figure by the name of Yamada Emosaku -- a painter and Japanese Christian who ultimately betrayed his fellows to the Tokugawa forces during the failed of the Shimabara Rebellio, consisting of disgruntled peasants and Christians led by the famous Amakasa Shiro in response to the religious persecution and generally oppressive policies enacted by the shogunate and some rather incompetent, tyrannical daimyo at the time.
https://wiki.samurai-archives.com/index.php?title=Shimabara_Rebellion
https://wiki.samurai-archives.com/index.php?title=Yamada_Emosaku
Notable takeaway 1: A traitor who's a painter is an obvious one.
And since I foresee there being multiple traitors being revealed, it'd only make sense that Oda would including references to several notable traitors throughout Japanese history ( e.g. Akechi Mitsuhide, Minamoto no Yoritomo's betrayal of his famous brother Yoshitsune, etc...). In short, the likelihood of Kanjuro being
a traitor is extremely high regardless.
Notable takeaway 2: Recall Oden's note on Kanjuro suffering from past persecution. Upon reading that, one of the immediate thoughts that entered my mind was that Oda would tie the character to in-story allusions to Japan's sordid history of religious persecution againt the "Kiri-shitans," something I knew he'd eventually be depicting in some form throughout this arc.
And we've seen just that: crucifixions, persecution of non-humans, Yasuie's own Jesus overtones...and when you consider Hiriluk's own cross motif, it suddenly ups the chances of his inclusion into the plot, don't it?
Doesn't end there tho. Denjiro's "Dozing" Inemuri Kyoshiro's identity is itself a likely reference to the famous "Sleepy Eyes of Death" film franchise centered around the eponymous Nemuri Kyoshiro aka the Son of the Black Mass, fathered by a fallen Christian foreigner during a Satanic ritual, leading to the character developing a rather bleak, cynical outlook on life and a particular distate for Christianity in general. Fittingly enough, the role in the most popular series of films was played by a famous kabuki actor. Ichikawa Raizo VIII
https://glitternight.com/tag/sleepy-eyes-of-death/
https://en.wikipedia.org/wiki/Ichikawa_Raizō_VIII
But wait, there's more
With Gecko Moriah likely to return to Wano to settle the score with Kaido as many have been predicting, I believe it's but a given that Oda's gonna throw in a tribute to this other notable franchise: the Makai Tensho series of novels, film, anime, and manga. Some might be familiar with the popular film starring Sonny Chiba with the alternate title of "Samurai Reincarnation", and others more through the "Ninja Resurrection" titled anime/manga form.
General summary: vengeful Shimabar survivor Mori Soiken plots revenge against Japan by using black magic to resurrect an undead of famous warriors and figures, notably with fallen Shimabara leader Shiro Amakusa taking the lead in all the various canon, now transformed into a vengeful force of evil. Notable Christian convert Hosokowa Gracia would likewise add to the "vengeful Christian" element in the film version.
https://en.wikipedia.org/wiki/Samurai_Reincarnation
https://en.wikipedia.org/wiki/Makai_Tensho
https://en.wikipedia.org/wiki/Amakusa_Shirō
https://en.wikipedia.org/wiki/Hosokawa_Gracia
So yes, big ties the history of Christianity in Japan.
Bonus: spiraling down the rabbit hole of rampant conjecture here, but given Kanjuro's hair-collection habits and the whole Christianity theme, I wouldn't be surprised if certain legends ( more a likely hoax really, but anyways ) concerning Jesus having not only travelled to but lived out the remainder of his life in Japan, bringing along with him a lock of the Virgin Mary's hair.
https://www.smithsonianmag.com/history/the-little-known-legend-of-jesus-in-japan-165354242/
Bonus trivia: What with Kanjuro being a painter and all, I'd be remiss in not pointing out that one other notable keepsake Jesus brought with him in the above legend was the severed ear of a twin brother named Isokiri who'd sacrificed himself by taking Jesus' place on the cross. Yeah.
Anyway, only reason I bring it up is because it instantly brought to mind everyone's favorite emo painter, Vincent Van Gogh, famous for severing his own ear after a dispute with a fellow artist and offering it up as rather strange token of love to a prostitute.
https://qz.com/823588/why-vincent-van-gogh-cut-off-his-hear/
How would this all weave into Kanjuro's tale? I'm not even going to touch that one yet lol
Notable takeaway 3: It's recorded that Emosaku was trained as painter by European missionaries. Multiple different ways this could play out under Oda's pen in this hypothetical scenario, but it further lends weight to the possibility that Kanjuro's interaction with some foreign party selling black market goods could factor heavily into his story.
Notable takeaway 4: Like his fellow Three Great Unifiers, Oda Nobunaga and Toyotomi Hideyoshi, Tokugaw Ieyasu actively engaged in persecuting Christian minorities in Japan, though initially not to the same brutal extent as the other two. Whatever relative restraint he may've demonstrated early on would eventually evaporate in light of the threat he perceived Christianity as osing in the wak eof Akamakusa's rebellion.
Needless to say, it's obvious that Shimotsuki Yasuie and Kozuki Oden are blatant ( if ersatz ) analogues to the real life Ieyasu and Nobunaga, albeit predictably reconfigured and flipped around as Oda enjoys doing. So then, if Kanjuro is presumably the One Piece incarnation of Yamada Emosuke, it thus further points to Kanjuro potentially having a rather complicated relationship with not just Oden but Yasu as well.
Everything I've outlined about Kan potentially being involved with outside goods and/or traders suddenly starts sounding more credible when you consider that Yasu was in charge of the only open port at one point in time in Hakumai, further connecting the two. And as I pointed out, it was Kanjuro who ultimately volunteered to bury Yasu, leading me to suspect he has some shady intentions for Yasu' afro..
Hell, just for the hell of it, I'm gonna baselessly speculate that one scene in which Kan and Shinobu failed to recognize Yasu isn't the first occurrence of one failing to discern the identity of the other; I'll go out on a limb and postulate that Yasu had already once met Kanjuro before prior to his fateful introduction to the young Scabbards. Their first meeting was probably a rather rocky one, and Yasu failing to recognize Kanjuro in light of the changes wrought by the latter's ( again, purely speculating here ) sickness probably didn't improve matters...
In short, Kanjuro may've once held a grudge against not just Oden but Yasu as well.