Looking for an anime...

So I remember this anime that I watched before, but I can't remember what it's called and idk if it came from a manga or not. It's main character is a boy in high school, but not a normal high school. It was a high school that teaches students how to assassinate people I think. He was friends with a priestess like student and whenever he saw panties or something ecchi he changed into a different type of person. Any of this ring a bell?