After losing his father, son Kenichi lives alone with his mother, Shinobu. One day, he catches her wearing a thong, noticing something he never expected. Quiet and plain in everyday life, he becomes curious about why his mother would wear such revealing lingerie. Pretending to leave the house, Kenichi sneaks around the back and witnesses his mother having sex with her lover. The shocking discovery sends ripples through his mind. Convinced that she's betraying both his late father and himself, Kenichi is overwhelmed by intense, conflicting emotions he's never felt before.