E-1: Karma Akabane / A sadistic boy with the class's top combat ability and a genius intellect. E-2: Yuma Isogai / Male class representative. Poor but handsome and sincere, he is the class's moral pillar. E-3: Taiga Okajima / A pervert who channels his passion for adult magazines into assassination and intel gathering. E-4: Hinata Okano / Former gymnastics club member. An acrobatic assassin with incredible physical abilities. E-5: Manami Okuda / A science genius. Shy, but supports assassinations by concocting poisons and chemicals. E-6: Megu Kataoka / Female class representative. Reliable and tomboyish, excels at swimming and sports. E-7: Kaede Kayano / Nagisa's partner. Actually hides a 'certain secret' that holds the key to the story. E-8: Yukiko Kanzaki / The class idol. Appears refined, but is actually a master of arcade games. E-9: Masayoshi (Justice) Kimura / The fastest runner in class, a specialist in stealth and reconnaissance. E-10: Hinano Kurahashi / A nature-lover who provides healing vibes. Rich in knowledge about insects and the outdoors. E-11: Nagisa Shiota / The protagonist. Small and unassuming, but hides a pure 'talent for assassination.' E-12: Sosuke Sugaya / The artistic type. In charge of art, including creating disguise masks and camouflage painting. E-13: Tomohito Sugino / Former baseball player. Friendly personality, aims for assassinations using his baseball pitching speed. E-14: Kotaro Takebayashi / The glasses-wearing otaku. Excels at data analysis; later inherits his family's hospital. E-15: Ryunosuke Chiba / A boy whose eyes are hidden by his bangs. The male ace long-distance sniper. E-16: Ryoma Terasaka / Leader of a group of large delinquents. Rough, but dependable in a crisis. E-17: Rio Nakamura / A gal-style girl fluent in English. A prankster who gets along well with Karma. E-18: Kirara Hazama / Loves reading and is very negative. A gloomy girl who enjoys curses and the occult. E-19: Rinka Hayami / A tsundere girl. The female ace sniper with high dynamic visual acuity. E-20: Sumire Hara / Plump physique. Has a motherly, inclusive nature and is skilled at cooking. E-21: Yuzuki Fuwa / A shonen manga fanatic. Uses her manga knowledge to see through incidents and tricks. E-22: Hiroto Maehara / The class's top ladies' man and playboy. Best friends with Isogai. E-23: Koki Mimura / Unobtrusive, but has high video editing and directing skills. E-24: Takuya Muramatsu / Part of Terasaka's group. His family runs a ramen shop, and he hones his cooking skills. E-25: Toka Yada / Has an excellent physique and learns the art of negotiation (honey traps). E-26: Taisei Yoshida / Part of Terasaka's group. His family runs a bike shop, and he excels at mechanical modding and driving. E-27: Ritsu (Autonomously Intelligent Fixed Artillery) / An AI transfer student. Resides in the students' smartphones as an app. E-28: Itona Horibe / A transfer student with tentacles. Later discards them to utilize his engineering talent.

Koro-sensei / A mysterious octopus-like super-organism moving at Mach 20. A master teacher who raises his students while they target his life. Tadaomi Karasuma / An elite from the Ministry of Defense. A serious and dependable PE teacher who instructs in practical assassination techniques. Professor Bitch / A beautiful, skilled honey-trap assassin. Teaches the students conversational English and negotiation. Aguri Yukimura / The previous homeroom teacher. Deceased, she is the person who triggered the entire story. Akira Takaoka / A temporary instructor from the Ministry of Defense. A mad sadist who plotted to rule through violence behind a smile.

Akira Takaoka: A man from the Ministry of Defense who rules students through fear. The Second Reaper: The world's top hitman. Later modified into a tentacled creature. Professional Group: Assassins who attacked the students in the Okinawa arc, holding the cure hostage. Shiro's True Identity: The mad scientist who created Koro-sensei. The Root Cause: The person who turned Koro-sensei into a monster through human experimentation, creating all the distortions. Obsession: Driven by intense hatred for Koro-sensei, he manipulates Itona and the Second Reaper to attack repeatedly.