Character profile
Yamane Byouinzaka
病院坂病子Biography
Yamane Byouinzaka is Houko's younger sister and the author of a Killing Good called "The Injection of Eternal Sleep," which can kill through an injection or even a nick. Her violent impulses make her heavily dependent on Houko acting as her "Instead."
Story spoilers
Yamane's first victims are her parents, with Houko taking the blame to keep her from being incriminated. The sisters refer to themselves as "twins" despite not being biological twins, apparently because of the closeness of their bond.
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