Tsukuya is an unimpressive and talentless young man. On the other hand, his older brother is dating Sayuri and everyone is envious of the beautiful couple. Concerned about Tsukuya's well-being, his brother asks Sayuri to tutor him. During one of their lessons, Tsukuya accidentally touches Sayuri's body, which awakens his sexual desires. Despite Sayuri's initial pain and distress, Tsukuya ends up forcefully engaging in various sexual acts with her. From then on, Tsukuya continues to summon Sayuri and subject her to his increasingly deviant and relentless desires for hours on end. Initially resistant, Sayuri eventually succumbs to the prolonged foreplay and becomes a woman with a strong desire for internal ejaculations, while her feelings for Tsukuya's brother fade away.