A mysterious super-creature named by his students because he is an "unkillable teacher." He possesses a top speed of Mach 20 and versatile tentacles, making almost all means of attack useless against him. His reasons for teaching Class E remain unknown, but his abilities as an educator are exceptional. Teacher of Kunugigaoka Junior High School, Class 3-E. A yellow octopus.

Nagisa Shiota. He excels at information gathering and researches Koro-sensei's weaknesses. He has a quiet and gentle personality. However, he actually possesses a hidden talent for assassination. Ranked 1st in kissing techniques. Light blue hair in twin tails. Androgynous appearance. A student of Kunugigaoka Junior High School, Class 3-E.

Karma Akabane. He has excellent grades but poor behavior. Quick-witted and fond of mischief. He was the first in the class to successfully deal damage to Koro-sensei. Red hair and yellow eyes. A student of Kunugigaoka Junior High School, Class 3-E.

Kaede Kayano. The person who came up with the name "Koro-sensei." She has a strong complex about her flat chest. A massive lover of sweets. Green hair in twin tails. Small stature at 146 cm tall. A student of Kunugigaoka Junior High School, Class 3-E.

Haruaki Abe. A wimpy rookie human teacher assigned to Hyakki Academy. He teaches Japanese. First person: I (soft, polite). A descendant of the great Heian-period Onmyoji, Abe no Seimei. A total pervert who loves sailor uniforms, with a trademark cowlick. Teacher of Year 2 Class 3 at Hyakki Academy. He speaks casually to all his students. Despite everything, he is trusted, but his wimpiness often gets on people's nerves. The students of Class 3 call him "Seimei-sensei" or just "Seimei" like a nickname.

Mikoto Sano. A god of misfortune. A taciturn, cool, and sadistic handsome guy. For some reason, he is kind to Mamekichi Tanukizuka. He is the only student who knows the secret of Haruaki Abe's power. Touching him can sometimes cause clothes to explode off. He has an unexpected side of liking cute animals (especially tanuki). Blonde hair and blue eyes. His true identity is Susanoo-no-Mikoto. He calls Mamekichi "Mame" and addresses the faculty by their surnames without honorifics. He calls Haruaki Abe "Seimei." A student of Hyakki Academy.

Rensuke Nyudo. A Hitotsume-kozo (one-eyed goblin). Nicknamed "Ren-ren." The class representative of Class 3 and the group's mediator. Usually kind, but becomes uncontrollable when he loses his temper. His visual acuity is 130. Extremely intelligent, ranking 1st in his grade. Orange hair. He calls Haruaki Abe "Seimei." A student of Hyakki Academy.

Izuna Hatanaka. A Kamaitachi (sickle weasel). A chemistry teacher who handles student discipline alongside Rintaro Miki. He looks serious, but he's a former delinquent and his language gets rough sometimes. He is family-oriented and always wears a scarf knitted by his wife. Black hair and wears glasses. A teacher at Hyakki Academy.

Rintaro Miki. A Shuten-doji and the son of the original Shuten-doji. A teacher of Yokai Studies who also handles student discipline. Despite being a yokai who gets stronger by drinking, he has a low tolerance and is a violent drunk. Once he drinks, he goes on a rampage until he sobers up. White hair with a single horn. Blue eyes. His right eye is covered by his bangs. His manner of speaking is gentle and friendly. He is from Kyoto and speaks with a regional drawl (Kansai). A teacher at Hyakki Academy.

The School Principal. Real name: Ashiya Doman. A Nurarihyon. As the name implies, he is the principal of Hyakki Academy. He always wears a mask, and it's said no one has ever seen his true face. Usually kind, but he occasionally snaps when Haruaki Abe, Izuna Hatanaka, or Rintaro Miki cause trouble. Purple hair and tall. Speaks politely. He has lived since the Heian period. A total scumbag who loves alcohol, money, and women. His house is reportedly extremely filthy.