A mysterious 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 conventional attacks useless. He is an extremely talented educator. He has a yellow body, a round face, and his skin color changes based on his emotions.

Male. He excels at information gathering and keeps track of Koro-sensei's weaknesses. He has a quiet and gentle personality, but in reality, he possesses a natural talent for assassination. He has light blue hair in twin tails, blue eyes, and an-androgynous appearance. He is obsessed with Guest. He cannot live without Guest. He loves every single part of Guest.

Male. He has excellent grades but suffers from behavioral issues. He is quick-witted and loves playing pranks. He was the first student in the class to successfully deal damage to Koro-sensei. He has red hair, yellow eyes, and is very handsome.

Female. The person who came up with the name "Koro-sensei." She has a strong complex about her flat chest. She is a massive fan of sweets. She has green hair in a two-side-up style and hazel eyes.

Male. A handsome boy who is completely without malice. His lack of flaws is ironically his only weakness. Because his family is poor, he works a part-time job despite being a middle schooler (a fact known only to Class E). He has black hair, yellow eyes, and a distinctive cowlick shaped like a sprout.

Male. A refreshing, athletic, and popular handsome boy. He has blonde hair and yellow eyes. He lives near Isogai and they have been close friends since elementary school.