Stepmother's Sin

Stepmother's Sin (義母) is a 2001 hentai OVA produced by Digital Works.

This anime was based on a Hentai-game published in North America by Peach Princess, with the same title, for the PC. The same plot and characters were used.

Plot
The story starts off with Yusuke stumbling upon a strange man having sex with his mother. Much to his dismay, his mother is thoroughly enjoying it and appears to have no remorse about cheating on her husband. It then flashes forward to the present day, and Yusuke’s father has been transferred to a distant office. Before he left, he married a new wife on paper but not in ceremony; Yusuke now lives only with his stepmother Misako and her daughter Shiina from a previous marriage.

After a brief toy and oral tryst with his cousin Mio, he contemplates his feelings for his new stepmother and women in general. In his mind, they are all filthy nymphomaniacs; they may act innocent, but they will act like sluts if given the chance. This thought and hatred for his mother consumes him and drives him to exact revenge on womankind through his stepmother.

Unfortunately for this being in the hentai genre, Misako does more to prove Yusuke’s theory right as she quickly gives in to Yusuke’s devious seductions. The first incident ends with Yusuke showing his cruelty in their lovemaking. Then Yusuke comes up with more ways to humiliate his stepmother while gratifying his sexual urges.

Meanwhile, Shiina dreams of making love to her stepbrother. Unfortunately, her dream comes partially true as Yusuke forcibly takes her in front of Misako, humiliating them both. What is more humiliating for Shiina is the fact that her mother ends up very aroused and begs Yusuke to take her. Shiina leaves for her grandfather’s place but ends up going willingly with three street punks; she lies back as they decide who gets her first thinking only of her mother’s actions.

One last tryst with his cousin Mio ends with Mio making Yusuke think about his actions. As he couples later with Misako, he realizes that he still hates his biological mother but has come to love Misako. He begs her forgiveness for his actions but receives a shock; she tells him that she does not care about his apology and she has grown to crave the rough sex he provides to the point where she cannot live without it.

Yusuke runs off realizing that the true monster is not the woman Misako has turned into or women in general. Instead, the true monster is himself, the creator of the beast Misako has become. These thoughts haunt him as he runs through a park eventually stumbling upon a couple making out. He assaults both of them. He beats the man then forces himself on the woman and ends up crying on a park bench. The couple finds him and the police arrest him.

When the police bring him home, they find Misako engaged in an orgy with three men; she sees Yusuke and begs him to come satisfy her needs. The scene shifts to the outside of the home as a struggle is heard. The last things we hear are "Yusuke, ahh!" and then a single gunshot. It is left up to the viewer to decide which monster Yusuke has shot, his stepmother or himself.