Onna Kyoushi Yumi no Houkago

Yumi is a busty, dark haired beauty who knows how to give her students what they want. But unfortunately, she's never been good at getting what she wants and lately everything seems to be going wrong. First she has a nasty break-up with her fiance, and then she's sexually harassed by the Vice-Principal. One thing leads to another... and before she knows it, the VP and some very horny students trap her into a hot and heavy orgy. After ravishing her over and over again, they make her swear to become their secret sex slave. Now, Yumi's only hope is the reluctant Katsutoshi and his perky girlfriend Keiko. But even with their help, it'll be hard for Yumi to escape her bonds of sexual slavery, since everyone seems to be hot for teacher... (Source: AniDB)