Stepmother's Sin

Stepmother's Sin (originally Gibo) is a 2001 Hentai anime based on the Visual Novel Gibo by Guilty.

When Yagami Yuusuke was a little boy, he witnessed his mother having sex with a man who was not his father. Not shortly after, his father also discovered this, and divorced her and took his son. Years later, his father re-married to beautiful widow called Misako Yagami with a daughter, Shiina. However, the experience Yuusuke went through had changed him: he had become extremely misogynistic and saw all women as depraved. Soon he entrusted himself with the mission of corrupting his stepmother somehow to prove himself right.

Animated by Studio Y.O.U.C. Produced by Digital Works. Licensed by Central Park Media and Critical Mass Video for the English language.

Irony: In the anime, the dialouge of the Mysterious Gentleman and Mio stated Yusuke's Father never paid attention to Yusuke's Mother to the point they never have sex again for a long time aside from their last known sex which led Yusuke's mother to become pregnant and gave birth to Yusuke, this indicates Yusuke's Mother reason for having sex with the Mysterious Gentleman at the begining was to learnt more about sexuality to regain her husband's attention, as the Mysterious Gentleman told Yusuke's Mother, she needed proper sex technique to prevent her husband from having an affair. However by the time, Yusuke discovered his mother having sex with the Mysterious Gentleman, their sex is extremely passionate, Yusuke’s Mother moans as she asked the Mysterious Gentleman to thrust his penis in her vagina more intensely rather than learning proper sex technique, signifying the two has officially become lovers and their sex is now meant to consumate their love. In a great irony, Yusuke's Mother's intial fear that her husband may commit adultery which lead her to start her sex lessons with gentleman, she ended up becoming the adulterer herself.
 * Abusive Parents: Unintentionally and unknowingly, Yusuke’s mother had deeply traumatized her son forever emotionally by having sex with another man while her son is at home. It was on the day when Yusuke discovered her adultery, as a child when Yusuke returned home earlier than usual. Yusuke called for his mother, only to find her naked having sex with her lover, to his heartbreaking, sorrow, and despair, his mother was immensely enjoying the sex with her lover and shown to have absolutely no remorse about cheating on her husband. Even when the Mysterious Gentleman point out that Yusuke may discovered their adultery, Yusuke’s Mother conveniently dismissed with the excuse of Yusuke being outside collecting insects. Ultimately, she no longer cared about Yusuke as not only would she risked being caught by Yusuke during her sex sessions, flashbacks in the ova showed when she divorced her husband, she was perfectly content to give up custody of her son to his father to start a new life with her lover without any guilt or remorse as Yusuke's mother turn her back, taking one last look at her son with a nonchalant expression before walking away.
 * Adaptation Expansion: The original visual novel Gibo only showed Yusuke’s Mother seen in a flashback, Yusuke remembers a brief and heartbreaking memory of his mother’s adultery. During his childhood, Yusuke witness his mother having extremely passionate sex in standing reverse cowgirl position with her lover the Mysterious Gentleman whose face is covered, the anime ova significantly expanded to show and extended the scene of Yusuke's Mother committing her first adultery with various sexual acts and a short dialougue between Yusuke's mother and her lover contrary to the visual novel where they do not speak at all, the Mysterious Gentleman whose face is revealed groping and licking Yusuke’s Mother’s breasts, Yusuke's Mother performing an amateur fellatio on the gentleman who later gave Yusuke's mother cunnilingus before they proceed to have sex in missionary position, reverse cow girl position, standing sex position and finally doggy style position with Yusuke's mother replied to the gentleman the sex feels good. The anime dialougue explained Yusuke's mother's reasons for commiting adultery which was to prevent her husband from cheating on her as well as showed how Yusuke discovered his mother's adultery which Yusuke's mother came to fully enjoyed the sex with the gentleman as she asked her new lover to thrust his penis harder into her vagina.
 * Adaptational Villainy: In the visual novel, Yusuke's Mother served as a minor antagonist with little influence aside from causing her son some distrust issue towards women but Yusuke would still have a possibilty for a happy ending depending on the routes, however in the anime ova adaptation, Yusuke's Mother became the main antagonist of the Gibo hentai anime series as Yusuke’s Mother commiting adultery would have a tremendous negative impact on her son Yusuke, having witnessed with his own eyes his mother having sex with another man. This would led to Yusuke’s intense hatred for all women and subsequently the future tragedies Yusuke commited by raping his stepmother Misako and stepsister Shinna in the ova, transforming them into nymphomaniacs like what the Mysterious Gentleman had done to Yusuke’s Mother. Yusuke would eventually be arrested for raping another woman in public, later stealing a police gun to kill either himself or Misako who is in the midst of an orgy with strangers, thus Yusuke’s Mother infidelity had unknowingly destroyed her son’s future, ruining him forever along with Misako and Shinna.
 * All for Nothing: The Mysterious Gentleman's dialouge indicates Yusuke Yagami's Mother started having sex with him was to prevent her husband from commiting adultery by learning to have proper sex to gain his attention. However, by the time, Yusuke discovered his mother’s adultery, Yusuke’s mother has became a complete nymphomaniac, as she asked the Mysterious Gentleman to thrust his penis in her vagina more intensely as well as hurry up and cum inside her before Eizo returned home, more focus on having greater sexual pleasure which she absolutely enjoyed with no remorse on cheating on her husband to the point she neglect fully removing her panties which she left hanging on her right leg and still wearing her socks on while having sex. Ironically, all the sex lessons that was meant to prevent the chance of Eizo's infidelity occuring have been led Yusuke Yagami's Mother to officially commiting adultery herself.
 * Arranged Marriage: Yuusuke's father marriage with Misako is said to be purely commercial, though Misako isn't rich, so this must mean more exactly public image.
 * Becoming the Mask: Yuusuke ends up do having an Oedipus Complex for Misako as they become closer instead of only pretending.
 * Bitch in Sheep's Clothing: Yuusuke pretends only to be a confused, hormonal teenager to Misako, only revealing his cruel colours to Misako when she has already crossed the line and is trapped between keep doing things with him or ruining her marriage.
 * Book Ends: The series begins and ends with Yuusuke watching his mother have sex with someone that is not her father. This pushes him through a murderous edge as he feels trapped in a cycle, but we never see the outcome.
 * Brother-Sister Incest: Shiina lusts after her own brother. Which makes no less traumatizing when he rapes her.
 * Buxom Is Better: Yusuke Yagami's Mother both in the game and anime possesses an extremely voluptuous and slim body with enormous breasts which are not only large but their shape are extremely beautiful and attractive. Her breasts are so huge, they are significantly larger than her lover’s hands and when Yusuke saw his mother having sex in a doggy style position, Yusuke’s Mother ‘s enormous yet extremely beautiful and attractive breasts charmingly and energetically bouncing up and down harmonously in unison. In a flashback of the anime even when wearing a modest blouse, her voluptous breasts would provocatively protrude as a huge bulge underneath the blouse. The same goes for Misako whose bust size won't lose to Yusuke Yagami '' s Mother
 * Conspicuous CG: Used several times to show liquids flowing, and even a curtain.
 * Downer Ending: No matter how you interpret the ending, it is this: even if someone was only injured or even the shot missed, Yuusuke has committed a horrible crime, Misako became sexually corrupted by him, and Shiina became a doormat which accepts having sex with strangers who hit her at the street. Their family life is ruined beyond salvation.
 * Extreme Doormat: Shiina becomes one in the end, so traumatized by Yuusuke's rape who she is willing to go alone with strange men to an hotel to have sex, presumably to stay away from Yuusuke.
 * Gainax Ending: Near the end of the hentai anime, we see Yusuke being brought home by the police only to see Misako and the three guys she previously had sex with. Suddenly, a gun goes off, leaving questions as to whether Yusuke shot his mother or himself.
 * Gone Horribly Right: Yuusuke wanted to prove Misako was a "slut". He did prove himself right. That also happens when he begins to feel genuine feelings for her, so he is traumatized again.
 * Hey, It's That Voice!: You'll never hear Yami "Yugi" Moto the same way again after hearing Dan Green as Yusuke.
 * Hot Mom: Both Yuusuke's biological mom and his stepmom, which is the biological mother of Shiina.
 * Yusuke's Mother is very beautiful with an extremely attractive body. Due to her beauty and immense sex appeal, her lover who already had vast amount of sexual experience with women first, have an extremely intense lust towards her, as he would visit the Yagami Residence daily to have sex with her everyday as they continued to engaged in adultery.
 * Kissing Cousins: Yuusuke maintains a carnal relationship with his cousin Mio, but it seems nothing more than that.
 * Oedipus Complex: At first, Yuusuke pretends to have this to press Misako into sex. And then later, he feels actual more filial love towards Misako as he has more sex with her, mixing it all together.
 * Parental Incest: Yuu and Misako commit several acts of incest, and she is his stepmom.
 * Primal Scene:
 * What cause Yuusuke's deep resentment towards all women, watching his mother have sex with a lover when he was only a child.
 * Shiina ends up watching her mother lusting after and having sex with her own rapist in Episode 2.
 * Sexy Discretion Shot: We never see what happened to the woman in the park, but she seems fine afterwards, so Yuusuke probably didn't go far with her.
 * Unwitting Instigator of Doom: Yuusuke's mother accidently created a rapist and maybe a murderer depending on your interpretation of the ending. Yuusuke definitely was going to try to kill Misako (or himself) at least.
 * Your Cheating Heart: What also annoys Misako about having a carnal relationship with the protagonist is being a married woman cheating on her husband.