After losing her husband, Reiko has been raising her son Ichiro on her own. Naturally, she is sexually frustrated every day, but one day she discovers a pornographic magazine about mature women in her son's room. Reiko learns that her son is aroused by women her own age, and she begins to feel indescribable emotions toward her son. Then, when she witnesses her son masturbating and his morning erection, Reiko's desire reaches its limit...