Naoko's husband has recently been forced to travel overseas frequently, leaving her feeling lonely and turning to masturbation as a habit. One day, her son accidentally witnessed her in the act and, driven by his affection for his mother, began stealing her underwear to masturbate himself. One day, when Naoko stopped by her son's room, she discovered him masturbating while calling out "Mother." Frozen in shock and arousal, Naoko suddenly realized she had begun touching herself as well. Rushing to her in panic, her son reached her just as the two crossed the line into forbidden intimacy. In that moment, a secret, intimate relationship was born.