The Cure Twist: The revelation that Kagero's poison is the cure for Jubei's poisoning is the emotional climax. Jubei refuses to sleep with her to cure himself (refusing to use her as a tool), but her dying kiss transfers the antidote, saving him. This subverts the 'damsel' trope by making her the savior.
Gemma's Immortality: The twist that Gemma is Jubei's former leader explains Jubei's cynicism. Gemma represents the ultimate corruption of the ninja code. His defeat—being encased in gold—is an ironic punishment: the immortal is trapped forever in the material wealth he valued over life.