Kengo Ishizuka, a male teacher with twenty years of experience, returns to Asazuka Academia—the high school where he started his career and first perpetrated sexual violence. Entrusted with overseeing an old building slated for demolition, he converts it into a private space for his sadistic pursuits. He has black hair and brown eyes.

He specifically targets female students and colleagues, beginning with Morimiya Saki, an intelligent student he identifies as promising. Through stalking, he uncovers her routines and vulnerabilities before expanding his focus to her friend Arisa, her mother Rie Morimiya, and fellow teacher Mashima Mikako. He discovers Rie was a victim from his past and that Saki is his biological daughter; this revelation fails to halt his actions.

His methods blend psychological manipulation, blackmail, and physical coercion. Using surveillance-gathered information, he forces compliance in the isolated building, conducting bondage, torture, and sexual assaults. He implements a "training" system to break resistance and foster dependency, merging physical torment with intermittent reinforcement to enforce submission. He threatens victims' loved ones to ensure continued participation, as when exploiting Mikako’s concerns for Saki and her marriage.

His background involves transferring schools after victimizing students, leaving behind loyal "trained" individuals. At Asazuka Academia, he encounters Mei, a former victim still devoted to him yet unaware of his return. His actions stem solely from a desire for control and domination, devoid of remorse or moral conflict. He exhibits no redemption or change, sustaining predatory behavior throughout the narrative.