Reiko Sawamura's son Yuu looks just like his father, and he confides in her about struggling to find a girlfriend. Wanting to support him in any way she can, Reiko accidentally witnesses her son masturbating. In that moment, she decides to help him by joining in and assisting with his masturbation. This act marks the beginning of their relationship, which quickly escalates into physical intimacy. Forbidden feelings begin to grow, and their bond deepens with each passing day.