Sumire lives with her husband and son Koichi. Her son has a daily routine of stealing Sumire's underwear and masturbating while looking at the photos. One day, Sumire witnesses this scene and peeks in. She asks him, "Why are you doing that while looking at my mother's photo?" but he confesses, "I want to do it with you, I've always loved you." After receiving constant advances from her son for a month, the mother can no longer resist and crosses the line with her son.