A father remarried Shiho, a woman with a beautiful, firm buttocks. As his son grew older, he started to be interested in his stepmother, and before he knew it, she had become his sexual object. One day, while Shiho was cleaning the floor, the son couldn't resist the sight of her beautiful buttocks... However, since then, the act became a daily occurrence, and Shiho would start to desire her son whenever she found out that her husband was coming home late.