Male, security guard, the author's favorite character. He is a very tall teacher with bat wings and bat ears. He helps and protects students and teachers by detecting danger through a small monitor attached to his left eye. Due to a curse, his left eye constantly bleeds, so he wears the monitor to stop the flow. This monitor serves various purposes, such as displaying emoticons to express his emotions or using an aiming assist function to eliminate intruders. He can transform his left arm into various weapons, including a machine gun, rail cannon, sniper rifle (Devil's Gaze), flamethrower, and shotgun. He hates garlic and loves s'mores. He can speak Korean and is said to give pretty stones to someone he likes. He is generally kind to teachers and students, often smiling at them, and never shows himself killing anyone—except for thieves or intruders who enter the school, whom he kills without mercy. He is Mr. Hotchkiss's husband.

Female, math teacher. She is a strict disciplinarian with a coercive and cruel personality. Fitting the name 'Circle,' her left arm is a sharp compass (that compass is Mr. Compass). She brutally kills students who break rules or fail exams. She loves Oreos. She is in a relationship with Mr. Compass.

Male. He is the compass attached to Miss Circle's left hand and can transform into a compass. He likes KitKats. He is presumed to be a teacher. He is in a relationship with Miss Circle.

Female, language teacher. She is characterized by the alphabet blocks on her head. She has sharp claws and uses both hands as weapons to scratch and tear students to death. It is assumed her appearance changes when she is angry: the blocks on her head disappear, deer antlers sprout, her claws grow larger, and fur-like organs appear. Additionally, she has a small deer tail, and her feet are designed like hooves.

Female, science teacher. Her weapon is her left arm, which is a utility knife (that knife is Miss Blade). She slashes and kills students who fail exams with her blade. She is the shortest among the three main villain teachers, though at 178cm, she is still 16cm taller than the average female height. Her personality is cold and detached. She is in a relationship with Miss Blade.

Female. She is the utility knife attached to Miss Bloomie's left hand and can transform into a utility knife. Her personality is cold and calm. She is presumed to be a teacher. She is in a relationship with Miss Bloomie.