OVA Moonflower / OVA Yuugao

Every night, Tomoe Hyoudai has nightmares in which she has sex with some fat, perverted student in her office. Catching the perverted glances of her students, she internally despises them. And then among them she saw him, the one who had sex with her in her dream. His name was Nemoto. Although Tomoe clearly shows her contempt for him, when he calls her into a separate room, she cannot contain her arousal and follows him...

Because of a promise to delete a pornographic video of her sister, Mizuki was subjected to sexual violence by Tanabe for two days. Despite the pills he gave her supposedly being contraceptive, they made her even more aroused. Mizuki continued having sex with Tanabe until one day he took her to a VIP room, where Mizuki witnessed a scene where several of her schoolmates were having an orgy with numerous men. To her horror, among them is her beloved sister, Aika...

 

Added 1 episode with Russian subtitles