The God of Death (2005)
Kuzuha Ryuuga is an average student with a girlfriend. He's kind and helpful to others. Suddenly he starts having desires and keeps seeing visions of himself brutally raping the girls around him. Afraid of himself he checks himself in to the nurses office where he meets Mizuchi a demon girl. She explains to him that he's actually a god of death and it's his duty to collect the souls of those around him. To do that, he must first break their minds.
Ryuuga then gives weapons to the punks in the school and has them take over and hold all the students and teachers hostage in the gym. They choose eight students to return to the main school which has been sealed with cement so there is no escape. If the students are caught they will be punished.
Let the game of hide and seek begin.