After responding to the summons of Momoka, the school nurse, the protagonist is compelled to participate in various sexual acts with her. Subsequently, the protagonist inadvertently catches Momoka's younger sister, Maron, masturbating. Upon being discovered, Maron retaliates by stripping him and performing hand and foot jobs. The situation escalates, and he ultimately takes her virginity. Eventually, the trio visits a public bathhouse, where they engage in a threesome.