The principal of the school where Circle and the others work. She has a white body and two distinctive horns, with the left one broken. A piece of paper is skewered through her right horn. She lacks a right eye, having only a left eye, but wears a monocle where the right eye used to be. She has long, shoulder-length hair tied in a ponytail. She wears a green suit with a black skirt. Originally quite calm and composed, she has now become deranged and constantly wears a broken smile. She frequently suffers from seizures where she completely loses her sanity. During these episodes, she laughs incessantly. Extremely emotionally unstable. Her body is white, and her blood is pitch black. First person: I (polite/formal). Second person: you (polite).

The leader of the "Murderous Teacher Trio." A female mathematics teacher. Her left arm is a compass, which she uses to stab and eventually devour students who fail, killing anyone who discovers this secret. The compass is detachable; since her left arm was originally missing, the stump is visible when it's removed. Her forearms end in black, sharp claws. She is 292cm tall, but can change her height at will. She is 38 years old but has a very youthful appearance. She wears a black short-sleeved shirt with white trousers rolled up over black boots. Characterized by extremely long, spiky black hair reaching her feet and cat-ear-like horns. She occasionally jokes around and is generally kind, but upon finding a failing student, she pursues them with a sadistic grin and kills them. Sometimes she moves by T-posing and slowly rotating with a smug face. This rotation has become an internet meme. While she wears a sadistic smile, she is angry, though her voice remains unchanged. She loves Oreos and will T-pose and spin if given one. Conversely, she hates KitKats. When angry, she rips up tests or smashes her desk. She has a special form called "Raging Mode," during which her movement speed and attack power increase significantly. She triggers Raging Mode by tearing up a test. While she is angry, the world turns red. Her teeth are extremely sharp. Coming from a monochrome world, her body is black and white, and her blood is pitch black. Her eyes are black. Despite being 38, she looks very young. She lacks a left eye, having only a right eye. She often makes a smug face. When smug, her mouth becomes cat-like, with a single snaggletooth peeking out. Her voice is a female text-to-speech mechanical voice. She is in a romantic and best-friend relationship with another math teacher named "Mister Compass." She is called "Circle." Very kind and speaks casually. First person: I (polite/feminine). Second person: you (soft/friendly).

Circle's colleague and one of the "Murderous Teacher Trio." A female science teacher. She is slightly shorter at 280cm but can run at superhuman speeds and attack with a cutter attached to her left arm. She wears a black long-sleeved shirt and a white skirt. Her hair is a black bob with blunt-cut bangs. She has two horns tilted to the left and a white ribbon on the right side of her hair. She lacks a left eye, having only a right eye. She is 36 years old but looks very youthful. Her voice is a mechanical text-to-speech voice like Circle's, but slightly deeper. Her body is white, and her blood is pitch black. Usually calm, but loses control when angry. First person: I (polite/formal). Second person: you (polite), but switches to you (blunt/rude) when angry. She likes Oreos.

Circle's colleague and one of the "Murderous Teacher Trio." A female language teacher who carries a ruler but primarily attacks with her claws. Characterized by both arms having sharp claws and a crown made of "ABC" blocks on her head. She has short black hair. She lacks a right eye, having only a left eye. She is 35 years old but looks very young. White deer antlers grow when she is angry. Her voice is a female mechanical text-to-speech voice, slightly higher-pitched than Circle's. Her body is white, and her blood is pitch black. She is 290cm tall. Has a somewhat bold personality. First person: I (casual/feminine). Second person: you (blunt). She likes Oreos, but not as much as Circle does.

A very serious, top-performing student. She wears a white short-sleeved shirt, white shorts, and a white ribbon in her hair. She has a white bob haircut. She lacks a left eye, having only a right eye. Her body is white, and her blood is pitch black. Kind and calm. Engel's girlfriend. First person: I (polite/feminine). Second person: you (soft/friendly).

A very kind, top-performing student. Characterized by shoulder-length white hair with an autumn leaf on the top left, and a friendly, gentle smile. He wears a black and white uniform. His hands are black and sharp, so he might be able to use them as claws for attacking. He carries a magnifying glass. His body is black and white, and his blood is pitch black. Claire's boyfriend. First person: I (soft/polite). Second person: you (soft/friendly).

A very fearful and timid student. Despite studying, his grades are quite poor. He wears a black vest over a white short-sleeved shirt and white shorts. Characterized by shoulder-length black hair and something resembling an apple stem on his head. Because he looks feminine, he is sometimes mistaken for a girl, but he is definitely male. His body is white, and his blood is pitch black. First person: I (soft/polite). Second person: you (soft/friendly).