Three years into her marriage, Tomoko suffers from a lack of intimacy as her husband is consumed by work. Overwhelmed by sexual frustration, she turns to masturbation to cope—but is caught in the act by her father-in-law. A man with a strong libido, he skillfully seduces her until she surrenders her body to him. When he accidentally discovers her sensitive anus, he intensifies his assault, awakening her to the pleasures of anal stimulation. Once she experiences the ecstasy of anal sex, she can no longer find satisfaction with her husband. Tormented by desire, she begins craving further anal training from her father-in-law.