Katsutoshi Yoshioka is a student at Seimei Academy whose childhood friend, Keiko Fujimura, lives with him after running away. He approaches his teacher, Yumi Hayama, seeking help for Keiko, unaware this request is a pretext to lure Yumi into a trap. Katsutoshi participates in taking Yumi to an abandoned building where she is restrained. Tasked with filming under the belief it's merely a prank to frighten her, he becomes horrified when Gondo sexually assaults Yumi. His visible discomfort and objections are dismissed. He continues filming under coercion as the vice principal joins the attack, witnessing Yumi's repeated rape.

He suffers ongoing psychological torment. At school, he observes Yumi's traumatized and distracted state but remains complicit due to blackmail by the vice principal and Gondo, who threaten Keiko's safety if he reveals the truth or fails to cooperate. This forces his silence and further participation, including a gang rape in the vice principal's office where he is pressured into losing his virginity to Yumi.

His internal conflict intensifies as Yumi's suffering escalates into a complete psychological breakdown and transformation into a sex slave, especially after her ex-fiancé Matsunaga joins the abuse. Driven by fear for Keiko and guilt over his role in Yumi's torment, he attempts to help Yumi by finding and destroying the original blackmail tape to end the exploitation. This attempt fails, resulting in his capture. Consequently, Keiko is forcibly brought in and subjected to sadistic punishment alongside Yumi. His actions reflect a struggle between protecting Keiko and the desire to rescue Yumi, culminating in a failed intervention that causes further victimization for both women.