Kumi Kanzaki, a married Milf, secretly masturbates in the bathroom, unaware that her son Atsushi has discovered her habit. Though he knows it's wrong, he can't resist the urge to spy on her. One day, Kumi asks Atsushi to help clean the bathroom. While assisting her, he accidentally splashes water all over her, soaking her clothes. Seeing her nipples through the wet fabric, Atsushi becomes overwhelmed with desire and can't control himself, giving in to his urges and assaulting her.