Battle Royal High School

Battle Royal High School, originally known as Majinden (魔人伝, lit. "Legend of the True Devils") is a manga series written and illustrated by Shinichi Kuruma. It was serialized in the Tokuma Shoten magazine Monthly Shōnen Captain infrequently between the May 1986 and August 1989 issues. Originally released in four tankōbon, Battle Royal High School was later re-released in two larger volumes on December 20, 2008.

Plot
A story about a high school karate master possessed by a demon lord who is his doppelganger and wants to enslave the world but first needs to destroy a demonic fairy who also wants to enslave the world and is possessing a demon hunter, and the high-tech temporal security officer who is trying to stop most of them. Or at least some of them. And there is also a love triangle.