Even when her son is at home, her stepmother Yuu has lewd sex with her father in the middle of the day. It's enough to make Yasuhiko, a student who is preparing for his entrance exams, erect. As this happens, Yasuhiko begins to think of Yuu as a "woman." Realizing this, Yuu, who has a strong sexual desire, accepts her stepson, and the two of them finally... Since then, the son has been craving his mother's body even when his father is at home, and they have sex in the morning...