Kekkou Kamen 2 ~Oshioki Densetsu no Maki~

In the sequel to to the first Kekkō Kamen, the player is no longer required to control the satanic protagonist of the previous game. Instead, the protagonist is a young substitute teacher (default name Ryusuke) who is perplexed at his discoveries in the high school he is invited to work for. As the title implies (shioki means "corporal punishment"), some teachers and students engage in bizarre sadistic activities. It's up to the player to decide how the new guy will fit in.

[From Moby Games]