Professor Pain

The students of Aoi College, who are all 19 by the way, have always suspected that Professor Ohse might be some sort of pervert or cretin, but no one could have guessed how depraved he really is. As it turns out, he's really a terrorist who decides to hold the entire campus hostage, and make all of its comely young lasses submit to his desire for torture and depravity. (Source: Anime News Network)