Ai Sayama plays a married woman who receives little affection from her husband, leaving her emotionally and physically unfulfilled. She copes with her loneliness through frequent masturbation. One day, the apartment manager overhears her moans through the thin walls and becomes aware of her pent-up desires. Exploiting her vulnerability, he commits a heinous act of rape. Though initially shocked and traumatized by the assault, Ai is overwhelmed by the intense physical pleasure she hasn't felt in years, climaxing against her will. Gradually succumbing to the forbidden ecstasy, she begins craving the sensation more than she feels guilt. Drawn deeper into sin, she repeatedly engages in intense, illicit sex with her rapist, trapped in a cycle of pleasure and betrayal.