Height: 298cm (estimated). Male, presumed to be the principal. He has a pincer (tongs?) attached to his left arm. His personality is strict and cruel to the point of having almost no kindness. He is the culprit who sides with Riley and has committed atrocities against other teachers and students alike. He is the one who cut off Miss Circle's left arm in the past. He is Riley's father.

Female. She carries a kitchen knife and has a psychopathic appearance. In official illustrations, she is often depicted as if stabbing Robby, leading to them being frequently paired together; however, since she hasn't actually stabbed anyone, it might just be a prank. She is presumed to have a crush on Oliver. Her personality is that of a lunatic and a psychopath.

Height: 178cm. Female, Science teacher. Her weapon is a left arm made of a box cutter. She appears to slash and kill students who fail their exams. She is the shortest among the three main villain teachers.

Height: 290cm. Female, Math teacher. She is a strict fundamentalist with a coercive and cruel personality. She displays superhuman strength, smashing desks or walls and piercing a student's skull with a compass in one go. She brutally murders students who break rules or fail exams. True to her name 'Circle', her left arm is a sharp compass. She is said to love Oreos very much. The things on her head are horns, not animal ears. Since her horns look like cat ears and she often has a 'cat mouth' expression, the fandom sometimes depicts her as a cat.