Kazuya Shinohara is a male student of unspecified age with multicolored hair and black eyes, fitting a typical Japanese school setting. He exhibits minimal academic interest, frequently dozing in class and drawing reprimands or physical discipline from his teacher, Katsuko Kurose. Despite his disengagement from studies, he harbors a pronounced attraction towards Katsuko.

His opportunity arises upon accidentally witnessing Katsuko and fellow student Jun Yoshioka in an intimate moment in an empty classroom. During this incident, he seizes Jun's mobile phone as blackmail material. Leveraging this evidence, Kazuya coerces Katsuko into sexual encounters, fulfilling his longstanding desire. He explicitly states no intention to disrupt Katsuko's relationship with Jun, even outwardly wishing them happiness, instead positioning himself as Katsuko's supplementary sexual partner within an ongoing dynamic.

As the coercive relationship progresses, Kazuya's tactics evolve beyond blackmail. He employs psychological manipulation and demonstrates sexual proficiency, contributing to Katsuko's increasing involvement despite her professed love for Jun. Reports suggest he develops genuine feelings for Katsuko, culminating in a marriage proposal. The situation culminates with Jun discovering the affair, though Kazuya's continued sexual access to Katsuko implies his objectives were ultimately met.