Koro-sensei

About Koro-sensei

Koro-sensei is a yellow, octopus-like creature who destroyed most of the moon and will destroy Earth next March, unless his own students kill him first. Moving at Mach 20 and regenerating from any wound, he is functionally unkillable, yet he spends the year as the most devoted teacher alive, tailoring lessons, costumes and encouragement to every child in Class 3-E. His past as the God of Death is the series' central mystery.

Appearance

Koro-sensei is a tall, bright yellow creature with a huge round head, a permanent wide grin and small eyes that vanish when he is pleased. Instead of arms and legs he has dozens of soft tentacles, which he uses to write on the board, cook and grade papers all at once. He dresses like a proper teacher in a black academic gown and cap with a small tie bearing a crescent-moon mark. His face changes colour with his mood, pink when embarrassed or daydreaming, black when truly angry, and his whole body is soft, stretchy and almost impossible to damage with normal weapons.

Personality

Koro-sensei is cheerful, theatrical and relentlessly teasing, with a weakness for sweets, gossip and embarrassing his students. Underneath the clowning he is a genuinely brilliant teacher: he learns every student's strengths and fears, writes personalised feedback at Mach 20 and pushes each child toward a future of their own. The assassination almost comes second. He loves praise, panics comically when his weaknesses are exposed, and keeps careful notes on his own flaws for the class to exploit. The warmer he becomes as a teacher, the harder the class's mission feels, which seems to be exactly his plan.

Background & Story

Koro-sensei appeared after an explosion destroyed most of the moon, leaving it a permanent crescent. He announced that he would do the same to Earth the following March, but first, for reasons he would not explain, he demanded to teach Class 3-E, the struggling 'End Class' of Kunugigaoka Junior High. The government agreed: the students became assassins-in-training, with a ten-billion-yen bounty on their teacher's head, while Koro-sensei promised not to harm them and to train them properly. Nothing about him is easy to explain, his body ignores normal weapons, he flies at Mach 20, and his past is a complete mystery to the authorities. What is clear from day one is that he takes teaching seriously, tailoring lessons, trips and encouragement to every student in the class he chose for himself.

Powers & Abilities

• Mach 20 Speed: Koro-sensei can move, fly and react at Mach 20, letting him dodge bullets, cross countries for lunch and grade a class's papers in minutes.
• Regeneration: His soft body rapidly heals from wounds, and only weapons made from a special anti-Koro-sensei material can truly harm him.
• Protective Skin Shedding: Once a month he can shed his skin in a single layer and use the husk as a one-time shield against a deadly attack.
• Tentacle Dexterity: His many tentacles can each perform a different precise task at once, from writing lessons to massaging a student's stiff shoulders.

Key Relationships

• Nagisa Shiota: The quiet student who keeps the class's notes on Koro-sensei's weaknesses, and the one whose growth he watches most proudly.
• Karma Akabane: The first student to actually wound him; Koro-sensei delights in Karma's traps and answers them in kind.
• Kaede Kayano: The cheerful student who gave him the name 'Koro-sensei', from korosenai, 'unkillable', which he happily adopted.
• Tadaomi Karasuma: The government agent supervising the class; Koro-sensei teases him constantly but respects his professionalism.
• Irina Jelavic: The professional assassin placed in his class as a teacher, whose failed attempts on his life he treats as entertainment.

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