Mother Yui was a beautiful, kind, and warm presence—someone her son could proudly boast about to his friends. However, she had a secret she never wanted her son to discover: secretly watching her masturbating in the bathroom. In stark contrast to her pure and gentle demeanor, the lewd, hidden desires she harbored gradually began stimulating her son's mind, driving him into uncontrollable arousal. How would these secret days change the relationship between mother and son?