Yumi runs a private tutoring school from her home, where she already has a physical relationship with one of her students. One day, her nephew Yusuke comes to stay at her house, and she begins to feel a new kind of excitement toward him. Yusuke is serious and morally upright, criticizing Yumi's affair with her student, but his innocence deeply moves her. Yumi whispers in his ear, "Once women pass 30, they all become horny," and their relationship gradually grows more intimate.