Kousoku Chojin

Haruki is a student at the prestigious private Morino High School, which he attends together with his beautiful sister, and where he leads the drama class. One day, Haruki discovers a strange toupee that transforms his body. Unbeknownst to him, he has gained special powers and comes into contact with a strange violent world that is hidden inside the school. Now he must understand what's truly going on there, at the same time trying to "score" with every girl he meets - be it student or teacher...

[From Moby Games]