Random plot twist theory:
Kanjuro is no traitor, but his acting capabilities fooled everyone in this war, including the readers.
He will die, but he will reveal the truth and give some crucial information to the Scabbards.
And he probably let himself get stabbed by Kiku on purpose.
Or to add more dramatic effect, Kanjuro would hold Kiku's blade, and do a seppuku using Kiku's blade.
He feels ashamed for fooling his ex-allies, and he considers this his last mission that gave his life purpose.
With that, he died as both Kozuki and an ally to the Scabbards.
