Mother and son incest drowning in discipline

A year has passed since my father passed away in a traffic accident. Hiroshi's mother-in-law Keiko's discipline towards Hiroshi becomes more extreme day by day. As punishment for soiling his pants, he is forced to wear a diaper, taught how to wash his clothes in a way that satisfies his desires in the bathroom, and is even shown having sex with a friend right in front of him... One day, Hiroshi begins to have doubts about his grandfather, who frequently visits his house. Hiroshi then learns the real reason why his mother disciplines him so harshly...