After separating from her husband, Natsuko lived with her son Masaki. One day, she was asked to take care of a friend's son, Yuusuke, and the three began living together. Masaki, who had been monopolizing his mother, started to feel competitive towards Yuusuke for showing interest in Natsuko's large breasts and seeking affection from her. Yuusuke would sneakily seek affection from Natsuko, touch her large breasts, or beg to take a bath with her when Masaki wasn't looking.
