One day, Satoshi accidentally caught sight of his mother, Kyoko, masturbating in the bathroom, directing the shower stream to her groin. Entranced and aroused by the lewd scene, Satoshi devises a plan to get closer to her, convincing Kyoko the next day to let him help clean the bathroom. Kyoko's body, starved of intimacy due to her prolonged lack of relations with her husband, was filled with pent-up desire. Unable to resist Satoshi's sudden closeness, she eventually gives in, leading to an inappropriate encounter between mother and son in the steamy bathroom.