Based on the adult manga by Miyabi.
A guy wins a bet against his girlfriend and now she has to do whatever he says. He wants her to dress up as a cat, film a sex tape and fuck her out in public. You know, standard stuff.

Ep3 – The prideful and well-endowed teacher Wakatsuki Risa gathers the gaze of male students everywhere she goes within the school. However, she masturbates chronically and is discovered by some students. Blackmailed, she submits to their desires. Trained into becoming sex toy, she is even used by the janitor and school principal.

This is a short released as part of the 2006 boxset.
On a late evening, student Kurumi Imari is leaving her Academy classroom. As she makes her way down the hallway wearing her backpack, a male student is secretly stalking her every move. He suddenly lunches forwards and grabs the girl by her breasts. She screams and tries to push him away, but he covers her mouth and holds down her arm behind her back.
Her fellow student drags her into a storage room and takes out his penis. Shocked, Imari tries to run, but he painfully grabs her by her hair and forces her to give him oral sex. Afterwards, Imari quickly tries to make a run for the door again without success. The boy again quickly grabs her by her breasts and starts groping them. He proceeds to strip off her clothes and rapes her.
After the boy licks her feet and continues having sex with her, Imari stops resisting and gives in to her arousal. She starts riding her attacker willingly, and even affectionately licks him back.
Finally, the boy ejaculates over Imari’s half naked body. He grabs her striped panties and puts them in his pocket before walking out and closing the door, leaving behind a panting and soiled Imari.

Yuuto has taken service in the Ijiyuuin household to atone for his father’s misdeeds. He works hard and catches the eye of Serena, the 2nd daughter of the family. Utilizing her voluptuous body, she entices Yuuto. However, Selena is actually a vampire, and her partners don’t live beyond one day.

If you manage to stay a virgin till you are 30 years old you will become the next family head. However, the candidate for the next family head Teshirogi Naoki was being tempted by the women surrounding him. Will he be able to go through many trials and become the head of the family…?!

Before she got married, she was a playgirl who made love with numerous men. But she thought such a life was meaningless, and married an honest man. While she is spending a peaceful life, she happens to meet an ex-lover.
Source: AnimeNfo

The hero is an “ordinary student,” Tsukui Shinichi, now in his senior year. A long-lost childhood friend, Ayase Aoi, moves in next-door and transfers into his school. Shinichi can’t quite remember Aoi, which upsets her quite a bit. Her good looks attract the attention of Shinichi’s comic sidekick, Yamashita Satoshi, and the school playboy, Kanzaki Kotoro. While Shinichi and Aoi spar over a potential relationship, Shinichi crosses paths with and then beds other students, including a clumsy genki girl, Fujiro Mami; an aggressive vamp, Ebina Mika; and the president of the Flower Arrangement Club, Hayama Reiko, before finally ending up in the arms of his destined True Love.

A school where having sex replaces a normal grading system. The one at the top of the sex list gets the grades.