Bible Black School of Black Magic (2001)

The series revolves around a certain high school rumored to have been the base of operations of a coven several years ago (pre-2000). The school's unofficial "Witchcraft Club", as they called themselves, practiced black magic in the underground basement hidden away at the institute. Teachers, students, professors, and staff practicing the dark occult religion involving incantation sex, and sacrifices upon their innocent victims is a common and recurring theme in all things Bible Black.

Bible Black was originally created as a bishoujo game by ActiveSoft in the year 2000. The hentai game itself never made it outside of Japan, except as a package deal with the first anime in the United States, at least until recently, but the popularity of the game led to a series of hentai anime OVAs like Bible Black, and Bible Black Gaiden. Despite the age of the game and the hentai movies which sprung off the series, it remains one of the most popular hentai series ever made.