Mayu and her husband are openly affectionate, often cuddling even in front of their adult son Kiyoshi. After repeatedly seeing their intimacy, Kiyoshi begins viewing his mother as a woman and lets his desire build. When his father leaves on a business trip, he confines Mayu in a room. She initially resists his disturbing behavior, but gradually yields her voluptuous body and begins teaching him tender sex in her role as his mother.