The Main Characters (Koro-sensei) | Kunugigaoka Junior High School: Teachers and Students of Class 3-E | Kunugigaoka Junior High School: Faculty and Students of the Main Building | Assassins and Other Characters
Koro-sensei (殺せんせー Korosensē)
Also known as: Octopus (タコ Tako), The Reaper (死神 Shinigami, lit.: "God of Death")
Voiced by: Masaya Onosaka (Japanese, vomic), Tomokazu Seki (Japanese, event anime and J-Stars Victory VS), Jun Fukuyama (Japanese, TV anime), Sonny Strait (English) Foreign VAs
Portrayed by: Kazunari Ninomiya
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"Let's have an assassination that will make people smile and puff out their chests with pride. Each and every one of you can do that. You are talented assassins with hidden strength. That is advice from your sensei, as a target."
A mysterious octopus-like creature who was responsible for obliterating 70% of the Moon, leaving it a permanent crescent and also currently plans to destroy Earth after teaching the class for a year, and the homeroom teacher of Class 3-E of Kunugigaoka Junior High School.
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A - K
- Abusive Parents: Of the emotional neglect variety. While he was "fair but firm" to his disciple as he raised him, Koro-sensei never once "looked at him", according to Aguri. To which his disciple realizes that he's nothing but a tool to his mentor, leading to his betrayal of him.
- The Ace: Not only is he an amazing teacher, but with his powers, he can flawlessly perform pretty much any task in flying colors, even the most implausible ones. The yearbooks and personal guides he whipped up for his students before his death showcase this way better than words can.
- Affably Evil: For a being who wants to destroy the world, Koro-sensei doesn't act like it. Back when he was the original Reaper, he was really polite and charming for a master assassin.
- Animal Motif: The octopus. Like the animal, Koro-Sensei has several tentacles. He can also change his skin colour at will, which he uses both for communication and for camouflage.
- Apocalypse Maiden: What he actually is. He Was Once a Man, but antimatter experiments done on him turned him into a living bomb of world ending power.
- Arc Symbol: The permanent crescent moon, symbolizing Koro-sensei, often serving as a reminder of just how powerful he is. It is revealed much later that Koro-sensei had appropriated the crescent moon for himself as he took the blame for the moon's destruction, having sewed the symbol on his tie. Additionally, as Nagisa notes in the epilogue, after Koro-sensei's death, the crescent moon slowly coalesces back into a sphere thanks to gravity; in essence, the crescent moon "died" with him.
- Attack on the Heart: One of Koro-sensei's greatest weaknesses is his heart, located right underneath his tie. When fighting against Kayano, Koro-sensei allows her to attack his heart (albeit not long enough for it to be lethal) in order to create an opening for Nagisa to distract her, thus letting Koro-sensei take out her tentacles before they fully exhaust her. Also, in the finale, Koro-sensei allows Nagisa on behalf of Class 3-E to assassinate him just before graduation day, by having Nagisa stab his heart.
- The Atoner: For both his failure to protect Aguri, his past as a professional hitman, and his inability to properly guide his apprentice, who betrayed him to the government and assumed his "Reaper" persona, Koro-sensei has decided to spend his last days teaching her students at Class 3-E to honor her dying wish of helping them become better persons, even as he takes to heart her lessons about what it means to love and look after someone.
- Badass Adorable: He is so friendly, goofy and kind and often joins his students in their antics. Also no military in the world can kill this guy who also used to be the world's greatest assassin.
- Badass Bookworm: Along with being a very knowledgeable educator, he makes quite a few nods to Shonen Jump, including wearing a Leaf Village headband one time, and firing a giant slingshot using the Gum Gum Slingshot.
- Badass in a Nice Suit: When he and his disciple (the current Reaper) did an infiltration mission — and was subsequently betrayed by the latter.
- Badass Teacher: Koro-sensei is an extremely competent and protective teacher, who uses his inhuman abilities to teach and protect his charges. Trying to harm his students is an unwise move. In the past he was this to the current Reaper/God of Death, although Koro sensei only viewed him as a tool to expand his own successes.
- Bad Liar: He's bad at covering up his weaknesses. While this may be partially intentional, it's also because as he became more of a tentacle monster he lost a great deal of his emotional control.
- Bash Brothers: Together with Karasuma-sensei in the tag game."The strongest creature and the strongest human. They're coming to attack us to give us more homework!!"
- Beast and Beauty: The Beast to Aguri's Beauty. While he was handsome before his transformation, he was still an amoral assassin. The beautiful and kindly Aguri brought out the best in him, and inspired him to do good and take care of her students after she died.
- Beauty to Beast: Was quite attractive when he was still a human.
- Be Careful What You Wish For: When Koro-sensei was still physically an ordinary human and being experimented upon, he admitted that he could have killed and escaped his captors on numerous occassions. However, because he was aware they were attempting to turn him into a weapon, he decided that it would be advantageous to him to attain the powers the experiments were giving him, and so he stuck around. Unfortunately, allowing the experiments to progress led to a point where the scientists deemed him too dangerous to live. His following escape attempt was fraught with so many deadly tactics to contain his power that it culminated in the death of Aguri, one of the people monitoring him who he'd grown to care for. In that moment he felt that his newly attained abilities were worthless.
- Because You Were Nice to Me: He became fond of Aguri because she was the first person to show him kindness and teach him what it meant to look after someone.
- Being Tortured Makes You Evil: Briefly after he had broken out of his cell until Aguri snapped him out of it.
- Beware the Nice Ones: He's usually the nicest teacher you will ever meet, but when someone threatens his students you better watch out.
- Beware the Silly Ones: Normally, he's goofy and fun-loving until his students are in danger or it's time to get serious.
- Big Eater: Combined with Sweet Tooth. Or anything junk-foody.
- Big Good: Zigzagged. He is supposed to be Class 3-E's target because he will supposedly blow up Earth next March like he already did with the Moon. However, he is also a great teacher and a kind, sensitive and respectful person who gets along with pretty much all his students and helps them and other people in every way he can, and his students' attempts on his life are more or less Played for Laughs. Ultimately played completely straight once it is revealed that he really didn't blow up the Moon.
- Birds of a Feather: His friendship with Aguri stems from the fact that they are both troubled young adults living in abusive conditions.
- Bizarre Alien Biology: Yes. Well, ish. He's born on Earth, he just doesn't look like it. From his color-changing face to his multi-purpose tentacles, with more quirks being revealed over time.
- Blithe Spirit: For a creature who intends to destroy the world, Koro-sensei is an expert in making people change their ways for the better. Karma, Irina and "Red Eye" are all examples people whose lives improved through his charisma and wisdom.
- Body Horror: It looks pretty painful when he shoots himself to prove a point. But especially his transformation looks outright terrifying looking at his arm being all messed up and fingers moving in all ways they shouldn't, and how he looks when he's rampaging throughout the facility he was tested in. One should be happy that he hid in the cave when the rest of his transformation happened.
- Bunny-Ears Lawyer: Moon/planet-killing, manga-drawing, supersonic, perverted, but really good teacher, anybody?
- Buxom Beauty Standard: Koro-sensei loves big breasts, and often takes a shine to Irina. The flashback arc reveals that this originated from seeing Aguri in a tube-top that exposes her ample cleavage.
- Character Development: Throughout the series, Koro-sensei undergoes a subtle, important shift in personality. Formerly the original Reaper, the greatest assassin in his time, he slowly acclimated to the responsibilities of a teacher and to empathy itself, only recently instilled in him by Aguri Yukimura, a gentle young teacher assigned to observe him during his confinement. This is justified, because the "tentacles" have an emotionally reciprocal relationship to their host, being affected by and feeding into the host's emotional state. In late chapters, Koro-sensei states that he wanted to be "full of weaknesses, easy to get along with" and able to "touch even the weakest of things, protect them, and guide them". This from a guy who responded to a reckless assassination attempt by threatening the students' families (though this is probably just a threat to make them not repeat another suicidal assassination).
- The Chessmaster: He's an extremely skilled strategist.
- For example, in the "Robbers and Cops" tag game, he and Karasuma are the cops and have to tag the class within an hour, but Koro-sensei has the given handicap to be in "jail" until the last minute. The students underestimate his extreme skills, and they realize that his handicap is even his advantage, since nobody can tag out the "arrested" students as long he's in the "jail".
- Even though Koro-sensei is easily tricked, he uses the moments where he's one-upped by his students to provide them with helpful advice. He teaches them how to evade Karasuma when they get out, implying that he might be deliberately falling for their tricks in order to give them more opportunities to gain experience and put his advice into action.
- This even goes back to his time as a test subject in Yanagisawa's experiment. While the Grim Reaper is being experimented on, he manages to almost immediately understand the science behind the experiment. He then subtly alters the reported symptoms he experiences in order to trick Yanagisawa and guide the experiment along the path towards giving himself a more powerful form...all without the "genius scientist" even realizing it.
- Cheshire Cat Grin: His signature smile never moves, even when he's talking.
- Chivalrous Pervert: He doesn't hide the fact that he loves women with big boobs, but he also defends Irina from a group of perverts who were harassing her and is an all-around good person, aside from that destroying the world issue. He has limits in his hobbies. He owns a stash of dirty magazines, but he insists he doesn't go farther than mailing the editors out of devotion when he is framed for going on a panty raid.
- Clark Kenting: When he wants to go out in public, he sticks a fake nose on his face, changes his skin color to a more normal tone, and puts on a wig. Amazingly, it works.
- Color-Coded Emotions: Physically so. Since Koro-sensei is almost always smiling, his emotions are read by his face's coloration and color pattern.
- Yellow: Normal
- Yellow with blushing cheeks: Very happy (usually, but not always, due to breasts)
- Green and yellow stripes: Mocking contempt
- Dark purple with X shape: Wrong answer face
- Orange with circle shape: Correct answer face (Two circles for perfect scores)
- Light blue: Sadness
- Dark blue: Shock/fear
- Red-orange: Angry
- Pitch black: Extremely angry
- Pink: Drowsy/relaxed
- White: Poker face/bewildered
- Blindingly-white glow: All his emotions mixed together
- Combat Tentacles: Comes with being octopoidal.
- Combination Attack: He combines all his emotional energies and experiences into one supercharged blast against the Reaper. Koro-sensei kills the Reaper and permanently paralyses Yanagisawa.
- Compelling Voice: He can whisper at high speeds in order to instill thoughts into people's heads. He does this to the class during winter break to make sure they keep up with their studies despite their troubles concerning his past.
- Cool and Unusual Punishment: He likes to punish failed assassination attempts by ridiculous means, such as dressing the would-be assassin in silly costumes, painting their nails, brushing their hair, placing strange objects on them, etc.
- Cool Teacher: He is a great teacher who is always there to motivate his students, protect them and have fun with them.
- Cosplay: In the anime, each episode ends with Koro-Sensei dressed up as the character with the most focus in the next episode, such as Karma or Irina. In the manga, each installment's title page has him in some kind of costume, some of which have generic themes but some of which are pop-culture characters (eg the class posed as in the iconic class photo image from the Battle Royale franchise, with Koro-Sensei as Kitano from the film).
- Crazy-Prepared: Dear Lord, but is he? The guidebooks he produces are just one (big) example.
- When he faces Asano Sr. with grenade-trapped textbooks, he reveals he has memorized every textbook in Japan.
- Dark and Troubled Past: The man who became Koro-sensei was an orphan from a brutally corrupt slum in an unnamed tropical country, who learned survival skills at a very young age until he became the legendary assassin simply known as the Reaper, until his disciple sold him out to the Japanese government, which proceeded to conduct antimatter experiments that would turn him into a Living Weapon. During this time he met Aguri, who helped him rediscover his humanity with her tales of her experiences as a middle-school teacher. Unfortunately, after an experiment to test the effects of aging on antimatter in a mouse resulted in the destruction of 70% of the Moon, head scientist Koutarou Yanagisawa decided to have him killed before he exploded next year. When Aguri warned him, he went on a despair-filled rampage in an attempt to escape, only to fail to protect Aguri from the tentacle of an antimatter container. With her last breath, she asks the heavily mutated Koro-sensei to look after her students.
- Death Seeker: Turns out, this is what the whole assassination arrangement with his students amounts to. Koro-sensei began his tenure with the knowledge that he was a ticking time bomb who would explode in a year, so he decided he wanted to instill as much knowledge as he could into the kids as he could in that time, ultimately desiring that he would meet his end at their hands before his expiry date. Initially, upon learning he was to die, Koro-sensei actually felt so much despair he was ready to let the world blow up with him, but Aguri's dying request that he teach her students ended up changing his outlook.
- Deface of the Moon: He blew up most of it prior to the story's beginning. Except he actually didn't, it was a bluff to motivate his students. Although the real reason the moon blew up is connected to the same experiments that led to his powers.
- Didn't Think This Through: Koro-sensei's habit of offering a handicap in assassinations as motivation for his students typically results in this reaction from him.
- Died on Their Birthday: Koro-sensei is killed in mercy by his students exactly one year to the day after he destroyed the Moon, on March 13. This date is also his designated birthday, given that his actual date of birth is unknown.
- Dirty Cop: Played for Laughs during a game of Cops and Robbers where he lets himself be bribed with a photo of a bikini-clad woman.
- Disappears into Light: He dissolves into countless particles of light after his students finally assassinate him.
- Doesn't Know Their Own Birthday: Having grown up as an orphan in the slums, he never knew his own birthday. Aguri Yukimura decided to celebrate his birthday on the anniversary of the day they met.
- Drama-Preserving Handicap: He isn't allowed to injure any of the students or staff as a condition to be allowed to teach to class 3-E. Never mind the human students, even Itona wouldn't stand a chance against him if he were willing and able to retaliate.
- During the Assassination Island arc, the students' attempted assassination of him forces him to use his ultimate defense, which renders him unable to move for twenty-four hours — just as several of his students are affected with a deadly virus, with the only antidote in the hands of someone that wants to kill him. This forces Karasuma, Irina and the healthy students to risk their lives to get the antidote.
- Dreadful Musician: Weakness #27 — He's tone deaf. His dreadful singing is powerful enough to shatter concrete. (Though he's able to sing the "Korosensei Drawing Song" without issue.)
- Eldritch Abomination: Averted. Even though Koro-sensei looks like a freaky alien octopus, he states that he was born and raised on Earth. As what human, animal, vegetable, or mineral, it is anyone's guess.
- Et Tu, Brute?: Back when he was the Reaper, he was sold out to the authorities by his disciple, who took on his name and reputation as his own.
- Invokes this trope in a hilarious way when he's accused of stealing the bras of big-breasted women in town; Isogai tries to defend him as a "normal pervert", but as he starts listing down Koro-Sensei's perversions, even he tells him to just "turn himself in".
- Even Evil Has Standards:
- Koro-sensei is not pleased when one of his students' collaborative attempt at killing him almost injures one of their own.
- When the students of another school kidnap Kayano and Kanzaki, he destroys said students for daring to touch his students.
- On a different note, he may be a pervert, but he'd never stoop as low as underwear theft and other such especially perverted acts.
- Evil Laugh: As the Reaper, when he overwhelms Koutarou Yanagisawa and his soldiers in his flashback story.
- Exact Words: He's going to destroy the Earth come March, but until then, he's going to be Class E's teacher. After all, he's going to blow up on March 13 unless he is killed first.
- Excuse Me While I Multitask: When people try to kill Koro-sensei he's usually doing other things, such as meticulously trimming his attackers' eyebrows or giving a fighter jet a polish in midair. When helping his students study for the midterms by flashing between them so fast he leaves an afterimage, he is also resting on a chair outside the classroom.
- Explaining Your Powers to the Enemy: Subverted. When he bothers to say anything at all, he only tells the basics, and often leaves out key details, like the fact that his mucus protects him from his weakness to water.
- Extreme Omnivore: Aside from his habit of flying around the world to enjoy cuisines from different countries, he has been seen eating pens, tissues, knives, sodium hydroxide, aqua regia, plastic explosives, you name it.
- Faustian Rebellion: Before his first day of class, he uses his newly-gained powers to rip the scientists that caused them a collective new one.
- Flash Step: Koro-sensei has a top speed of Mach 20. During his introduction to Class 3-E, he easily dodges Karasuma while meticulously trimming his eyebrows. When attacked by state-of-the-art fighter jets, he gives them a midair waxing. When attacked by Isogai, Yada, Mimura, Maehara, Okano and Kataoka with knives, he disarms all of them, then replaces the knives with tulips without them noticing.
- A Form You Are Comfortable With: The first chapter makes it clear that his current appearance is not his true form. Sans tentacles, his shadowy true form seems human-like. Averted at the revelation that the "tentacles", referring to all the artificial components of his body, are altered by and alter the host's emotions. He began having minor but uncontrollable changes to his expression and limbs during the experiments, although his form remained stable until his Roaring Rampage of Revenge; it may be impossible for him to control his shape enough to play this trope straight.
- Fragile Speedster: By his own admission, he's so physically weak that it would take just one person grabbing each of his tentacles to pin him down. Good luck grabbing his tentacles, though.
- Freudian Excuse: He became an assassin due to a horrific childhood, same as Irina.
- Fridge Brilliance: He goes through an In-Universe example when Karma discusses his plans for the future. At first, Koro-Sensei was iffy about a career as a bureaucrat being appropriate for someone like Karma, but, after Karma explained his logic behind his decision, Koro-Sensei took it back, and conceded that it was perfect for him.
- Friendly Enemy: To his students and his coworkers, he is polite, sociable, and encouraging, even as they try to kill him and he threatens to blow up the planet.
- Gadgeteer Genius: Has extensive skill and knowledge with machines and electronics. He was able to upgrade Ritsu's capabilities for a relatively cheap sum of money and also built a custom motorcycle with a frame made of wood.
- Game Face: When his face turns pitch-black, it means he's very angry.
- Genius Bruiser: He is impossible to defeat in single combat, and he teaches every single subject at once without being challenged in any way.
- Genius Sweet Tooth: He's a genius teacher capable of teaching multiple subjects at once, and he loves his sweets, usually seen eating them and spending his salary as a teacher on them. As revealed in the paperback manga releases, this one has a justification; tentacled beings require huge amounts of calories to maintain their tentacles, hence they will naturally be drawn to foods high in carbs and sugar.
- Gentle Giant: He's much larger than any human, but he's fairly harmless for a self-proclaimed world-destroying monster, even toward people trying to kill him. He was originally a ruthless assassin, but became a friendly teacher to honor Aguri's last wish.
- Great Gazoo: Koro-sensei's super speed and playful personality allows him to do all kinds tricks that makes him a opponent that is better to out trick if you want a chance to beat him.
- Go Out with a Smile: Fully expects to do this. And he does, smiling proudly to his class as he bids them a final farewell as they assassinate him.
- Gone Horribly Wrong: A super-powerful artificial creature, created to be the world's savior, now on course to destroy it in less than a year.
- Goroawase Number: Koro-sensei is sometimes associated with the number 56 (which can be pronounced as "Ko-ro"). His baseball uniform has "56" on the back, and one Imagine Spot of Koro-sensei and Itona together has the former holding a board with "56" written on it.
- Guile Hero: For all his power, he almost always solves problems with trickery rather than brute force alone, often to the effect of bettering his opponents.
- Healing Factor: Koro-Sensei, amongst other abilities, has the power of regeneration. Even if he gets hit with Applied Phlebotinum weapons, unless his body is almost completely destroyed, he'll recover in seconds.
- Heel–Face Turn: Underwent one in the backstory, after Aguri's unrelenting kindness inspired him to honor her last request and take care of her students, vowing to use his powers for good.
- Heel Realization: After Aguri's sacrifice, he realized that for all his gifts and skills, he'd never tried to use them to help people, only to kill.
- Helping Would Be Kill Stealing: Though he may guide and coordinate them, he lets his students handle problems on their own whenever they're capable of it, which they usually are.
- The Hilarity of Hats: He always wears a mortarboard that never falls off... and also looks amusingly small.
- Hiroshima as a Unit of Measure: Every few chapters Koro-sensei is given a character introduction that includes one of these comparing to his ability to travel at Mach 20. Some are fairly sensible (651.241 times as fast as Usain Bolt's 100-meter dash) while others are ridiculous (133,333.33 times faster than the speed of falling sakura petals).
- I Let Gwen Stacy Die: As he destroyed Yanagisawa's lab in his escape, Aguri tried to stop him with a Cooldown Hug, only for her to be fatally injured by the tentacle of an antimatter container. He became the teacher of Class 3-E to fulfill her last wish.
- I'll Kill You!: Koro-sensei threatens to kill the families of Class 3-E if any of them endanger one another during an assassination attempt, though from what is later learned about his personality, he was almost certainly bluffing.
- Immune to Bullets: As Irina found out, he cannot be hurt by lead bullets, as the bullets literally melt inside his body.
- Informed Attribute: He is supposedly an evil monster who intends to destroy the world, and only hasn't done so yet because it would be boring... or so the narrative says. He actually acts like a kindly sage, helping everyone around him improve themselves. The dissonance is so extreme it's hard to imagine that it's not Foreshadowing some kind of reveal. And indeed, he's far from evil — he just cannot help that he will destroy the world if he's not killed, as the antimatter in his body will explode when he dies naturally. He wants to be killed and wants to help Class 3-E to save the world and fulfill Aguri's dying wish.
- Invisible Streaker: Played for Laughs. After missing the train during the class field trip, Koro-sensei latches onto the side of the train and uses his invisibility to avoid scaring other people, but his students point out that a random set of floating, disembodied clothing is just as unsettling.
- Invisibility: A rarely used ability, and his clothes and anything he's carrying will still be visible. He makes himself transparent by changing the color of his skin to match his surroundings like a chameleon.
- Involuntary Shapeshifter: Koro-sensei transformed several times after drinking hazardous chemicals. In a more serious note, after Aguri warned him of his impending death and that Yanagisawa was more than willing to kill him to preempt what he has done, he was not able to control his emotions and let the tentacles consume him.
- I Was Quite a Looker: His backstory reveals that he was actually quite handsome when he was still a human.
- Jerk with a Heart of Gold: Koro-sensei wants to destroy the world and constantly teases his students for not being able to kill him, yet he always makes sure they get good grades and successes in life. As it turns out, he had no intention of destroying the world, but the antimatter cells in his body will make him do so unless he is killed first, while his job as teacher was part of a promise he made with the dying Aguri to help her students become better people.
- Kamehame Hadouken: He learns to concentrate the energy from his Absolute Defense form into large beams.
- Ki Manipulation: Shown in chapter 84. What's interesting is that he initially didn't know he could do that; he learned it during the Island arc.
- Killed Off for Real: At the end of Chapter 177, he's killed by his students before he can be killed by the government.
- Kryptonite Factor: A rubbery material that is not described beyond being "special" and able to disrupt his cells on contact. It can be fashioned into knives, BB pellets or clothes, and is apparently available in abundance.
L - Y
- Living Mood Ring: He can change his skin color and pattern to show his emotions, since he is otherwise always smiling.
- Living Weapon: Yanagisawa injected him with antimatter as part of experiments to turn him into Japan's One-Man Army. However, when a similar project on the effects of aging on a lab rat destroyed 70% of the Moon, Yanagisawa decided to hastily can the project, even if it means killing Koro-sensei, who only narrowly escaped through Aguri's warning and, ultimately, sacrifice.
- Lovable Sex Maniac: He loves big-breasted women and enjoys reading porn magazines, yet he's still a funny and caring teacher.
- Love Redeems: He used to be the Reaper, the greatest assassin in the world. When he met Aguri, her kindness made him understand what it meant to watch over others. He almost lost himself again after hearing he would die next year, but Aguri's death and her final wish made him decide to spend what little time he has teaching Class 3-E both as fulfillment of her dying wish and as his atonement.
- Major Injury Underreaction: He casually blows or slices off his own tentacles, sometimes several at once. Supposedly this causes emotional disturbance that slows him down for a while afterwards, but that's still way less of a response than such injuries warrant. Of course, he can regrow his tentacles after a few seconds.
- Master of All: As the Reaper, he's pretty much mastered almost every skill imaginable, in order to be a more effective assassin. He has complete knowledge of just about any subject, including a mastery of science that allows him to hijack Yanagisawa's experiment...while the Reaper himself is the one being experimented on.
- The Matchmaker: A chapter has Koro-sensei pairing up the students into boy/girl pairs of his choosing to explore a cave in a poor attempt to cause some romantic tension between them. He even refers to the scheme as Couple Setup. Somewhat subverted in that he doesn't actually want them to get together as much as he wants juicy romantic gossip that he could poke fun at them for and write a novel about later.
- Meaningful Name: As mentioned under Punny Name, his nickname is a pun of "korosenai" ("unkillable" in Japanese) and "sensei".
- Multiform Balance: His ultimate defense form makes him completely invulnerable. Not even the Anti-Sensei material will work; it will explode on contact with his shell. However, he is also immobile in this form for 24 hours, and he is afraid that somebody could send him on a rocket into outer space (though he admits that would be unrealistic, since sending him to space would take too long). So while this form is truly unkillable, he has reason not to make regular use of it, and it doesn't make his molting ability redundant.
- Mundane Utility: This is practically the entire basis for his character. Koro-sensei boasts an enormous number of extraordinary abilities and he uses nearly every single one of them to be a better teacher. Able to fly at Mach 20? Use your speed to visit different countries during lunch breaks in order to sample local cuisine. Able to create dozens of visual clones through sheer speed? Use them to divide your attention to give every single student simultaneous one-on-one instruction. Able to regenerate from even severe injuries in a matter of seconds? Use the ability to remove limbs to motivate your students to perform better on the next test.
- My Greatest Failure: Aguri's death led to his Heel Realization and motivation to teach Class 3-E. In the end, he also admits he was an improper teacher to his apprentice, who betrayed him and later became the second Reaper.
- My Greatest Second Chance: When Aguri's younger sister Akari/Kayano is killed at the finale, Koro-sensei has the knowledge and preparation necessary to save her life this time. After stopping his rampage, he tells his ex-apprentice that were they to meet in the afterlife, he would Raise Him Right This Time.
- Mysterious Past: The beginning chapters already throw multiple question marks on his true identity, such as his motivations to become a schoolteacher and flashbacks to a dying woman who made him swear a promise. The latter half of the series ultimately reveals that he was a test subject for an antimatter infusion experiment gone horribly wrong, and that the woman was Aguri, his first love, who encouraged him to spend his last days teaching Class 3-E.
- Neat Freak: Koro-Sensei has a bit of a hang-up with cleanliness. As mentioned before, he meticulously trimmed an assailant's eyebrows and waxed a fighter jet in midair.
- Never Given a Name: His upbringing was so poor, he never got a real name. Upon becoming an assassin he took on the title of "The Reaper," and Kayano recommends the nickname "Koro-Sensei."
- Nigh-Invulnerability: He is able to withstand fire from multiple high-caliber machine guns at once. Apparently, the only things that can seriously harm him are the special anti-sensei material and other beings similar to him, like Itona.
- No Sense of Personal Space: Getting really close to his students seems to a part of being a Psychologist Teacher. Just one example is wrapping up Sugino in his tentacles to evaluate the flexibility in the kid's joints.
- The Nose Knows: He has an incredible sense of smell despite not having a proper nose. Some close-ups reveal nostrils almost identical to his eyes.
- Not Me This Time:
- He's framed as being a Panty Thief, but protests his innocence, insisting that, despite being a complete pervert, he'd never go that far. This turns out to be the truth.
- Despite everything he did do during his time as the God of Death, he didn't actually blow up the moon, though it was the result of the same experiments that made him what he is now.
- Not the Fall That Kills You…: Averted, though it involves sudden acceleration rather than deceleration. Koro-sensei cannot accelerate as quickly as he normally would if he has to catch or carry a normal human being because their bodies couldn't handle the physical stress.
- Octopoid Aliens: He claims to be one at the beginning of the series though this is revealed to not be his actual form.
- Omnicidal Maniac: He plans to blow up the Earth, along with everyone living on it. Eventually subverted, as it turns out that he has no control over the antimatter cells within him, which will explode on March 13 unless he is killed first.
- One-Man Army: He's so powerful entire fleets have been sent to go after him, mostly to no avail. In fact, his backstory reveals that he brought a ten-year-long conflict at a country (presumably his homeland) to a standstill in a space of a week by killing two dozen members of the top brass.
- Only a Flesh Wound: Losing limbs may affect his speed, but having two gaping holes shot through his head seems to have no effect on his ability to think at all.
- Only Known by Their Nickname: When his students asked his name, he said he didn't have any name he could tell them, so they could call him whatever they wanted. Kayano then decided to call him "Koro-sensei". He never had a real name, since he grew up on his own in the slums in an unnamed tropical country. Before becoming "Koro-sensei", he was known as the Reaper.
- O.O.C. Is Serious Business: When the goofy, fun-loving Koro-sensei becomes angry and breaks out his Game Face, prepare for this lighthearted manga to turn very serious, very quickly. He lampshades it after his first battle with Itona, when he turns embarrassed after one of his rare bursts of anger, lamenting that it will ruin his reputation as a gag character.
- Papa Wolf: He is basically the father-figure that all of 3-E needs at this time in their lives, particularly those whoare not on good terms with their actual parents. Attack or bully his students and Koro-sensei will make sure you pay for it.
- Paparazzi: Where there's potential for spicy gossip (in particular Ship Tease material), Koro-sensei is at hand to take notes and/or photographs.
- Paper-Thin Disguise: Sure, he makes sure to hide his more inhuman details, but it's still impossible not to notice his giant, bulbous head and his cartoonish face.
- Parts Unknown: The name of the country where was born is never revealed. Given how horrible the place is described, it's probably not worth knowing about.
- Perpetual Smiler: He rarely breaks his constant smile, even when he was being experimented on by Yanagisawa, or as he allows his students to give him a dignified death.
- Post-Final Boss: True to the series's premise, he is this, but here the main "fight" is the students overcoming their emotions to give him a peaceful dignified death, not allowing any slightest chance for him to explode.
- The Promise: Koro-sensei is teaching the students in his class as a promise he made to someone. As he once put it, teaching all of his students seriously is much more important to him than the end of the world. He made the promise to Aguri Yukimura, Kayano's older sister and the class's previous homeroom teacher.
- Psychologist Teacher: Goes to extreme lengths to make sure that his students are able to resolve their own personal problems.
- Punny Name: Due to a lack of a name at the beginning of the series, Kayano came up with Koro-sensei as a pun with the Japanese words "korosenai" and "sensei" ("unkillable teacher").
- Real Men Wear Pink: He knows how to groom eyebrows, and he does so quite impeccably.
- Reasonable Authority Figure: Koro-sensei may plan to blow up the world, but he's really understanding as a teacher. If a student fails an assassination attempt, he'll sit down with them and discuss how they can do better next time in a constructive manner.
- Red Baron: When he was human, he was known as the Reaper, the world's greatest assassin.
- Red Eyes, Take Warning: When his face changes to black he drops all his usual goofy characteristics and becomes seriously menacing.
- Required Secondary Powers: Flying at Mach 20 requires a few other traits to work properly, such as hardening and streamlining of his body so that he can withstand the whiplash and G forces. Also, he has to use his tentacles to screen Nagisa and Karma when they travel with him so they don't get pelted by high speed dust.
- Remember When You Blew Up a Sun?: He brags about being the one who blew up the Moon. Except he actually didn't.
- Screams Like a Little Girl: His voice gets quite high when he's splashed with water.
- Secretly Dying: In Chapter 133 he reveals he's going to die anyway on March 13 even if no one manages to assassinate him.
- Self-Duplication: He can move so fast he can make selectively tangible afterimages. Chapter 12 shows him making one for every student in the class to personally focus on their weak subjects. He even leaves one outside to rest from all that work.
- Shipper on Deck: He, and the rest of Class 3-E, ship Karasuma/Irina.
- Showing Off Your Powers: Koro-Sensei's introduction is marked by him demonstrating to his students how impossibly powerful he is: which includes showing his super regeneration, super speed, and combat tentacles.
- Shut Up, Hannibal!: Gives one to Yanagisawa when he gloats about his students being his biggest weakness during his fight with Reaper 2.0.Koro-sensei: THAT IS PREPOSTEROUS! You're a fool if you think I'll believe it's that cut and dry! These children, they've risked life and limb to save me! What they've gone through just to be here tonight is extraordinary! Their determination... their unflappable spirit... students like these are the greatest gift a teacher could ask for! They are not a hindrance! They are not a weakness! They are my class, and I am proud of each and every one of them! Call it what you will, but when the chips are down, I will give my life to protect them!
- Signature Laugh: "Nurufufufu."
- Silent Scapegoat: He isn't the one who blew up the Moon as he claims – it was a lab rat transplanted with antimatter generating cells, sent on a satellite to the Moon as part of an experiment to test the effects of aging on the cells which had Gone Horribly Wrong.
- Slasher Smile: His Game Face color: Pitch Black.
- Slave to PR: If there is one thing he will avoid more than death, it is disappointing his students. He wants them to see him as a trustworthy individual who is sincere in his desire to teach them to succeed in life (and in killing him). This is exploited by all those who want to kill him (including his students) such as when Shiro framed him as an underwear thief, and he ran headlong into a trap to clear his name after seeing how disappointed his students were in him.
- Smug Super: Well, yes. No chapter is missing without him boasting that he's unkillable. He even has a smug face, where several green stripes cross his face.
- Star-Crossed Lovers: With Aguri Yukimura, Akari/Kaede Kayano's older sister and previous homeroom teacher of Class 3-E.
- Stealth Mentor: Many times, Koro-sensei's lessons have multiple reasons behind them, always working to help his students grow as assassins and people.
- Stone Wall: His Ultimate Defense technique takes this to an extreme: He releases most of the energy and matter in his body in an explosion that blows away nearby enemies, then condenses said energy and matter into a ball-shaped barrier around him. This makes him absolutely invulnerable, but leaves him as a talking head for 24 hours.
- Street Urchin: As a child, he grew up on his own in a brutally corrupt slum in an unnamed tropical country. Due to his violent background, he became an assassin eventually known as the Reaper.
- Suicide by Cop: He's training the students to assassinate him by the end of the school year, but he downplays the suicide aspect by actively resisting assassination attempts with his incredible speed, making it an actual challenge for the students. He plays the end goal absolutely straight, though, as he's rooting for his termination so that he doesn't destroy anything more.
- Super Drowning Skills: Because his body is sponge-like, it absorbs water quickly, weighing him down on water.
- Super-Speed: Koro-sensei, as previously mentioned, can move at Mach 20. He eats shaved ice he personally gathers from the North Pole. He eats Chinese food on his lunch break... in China.
- Suspiciously Specific Denial: In chapter 43.Koro-sensei: "...I mean, I just don't really feel like swimming. And it's not like my tentacles get all bloated underwater and I can't move or anything."
- Tall, Dark, and Handsome: When he was a human, he was a really handsome black-haired man.
- Tentacle Hair: Before fully mutating into his current appearance, upon finding out the scientists that experimented on him intend to kill him, Koro-sensei suddenly manifests tentacles all over his body, predominantly on his head, completely replacing his black hair with long, white tendrils.
- Terrible Artist: One of his minor weaknesses, he can only do simple art. And he still challenges Sugaya, the best artist in class, to making henna tattoos.
- This Loser Is You: The Season 2 Premier, and Chapters 74-76, in which Koro-Sensei attempts to play Shipper on Deck for his students, ends up being a Take That! to real life shippers. His students end up finding it creepy that he's so interested in trying to pair off a bunch of kids.
- Together in Death: In the epilogue, Kayano imagines that somewhere he and Aguri are now watching over Class 3-E even after seven years.
- Tombstone Teeth: Koro-sensei sports a brick-toothed grin that only adds to his cute-but-creepy Smiley Face-with-tentacles appearance, and is the cherry on top of him being a borderline Eldritch Abomination with enough power to destroy the planet. When he gets angry, however, his teeth turn into fangs. Even when he was human, he'd sport a brick-toothed grin for comical effect when he was being perverted.
- Too Powerful to Live: He is this to the entire world. Even though his chances of actually destroying the world are less than 1%, world governments refuse to even consider the possibility of letting him live. Even discounting that, his abilities are so game-breaking he can do whatever he wants, and no one would be able to stop him. This is why all later examples of beings with his power were deliberately given either critical weaknesses or shortened lifespans.
- Tragic Keepsake: His necktie was a birthday gift from Aguri Yukimura, the woman he loved and who gave him a birthday.
- Tragic Monster: He's about to destroy the Earth just like he did with the Moon... and it's not completely of his own free will. For one, he's actually taking the blame for an antimatter-infused lab rat destroying the Moon, while the same cells in his body have turned him into a walking time bomb.
- Tranquil Fury: When Kayano was impaled by Number Two, he barely uttered a word or raised his voice despite his absolute fury. He simply concentrated all his power into one final, devastating attack and made short work of Shiro and Number Two. It's less tranquil in the anime, where he emits a roar of uncontrollable rage for several seconds as he turns white.
- Villain Protagonist: He destroyed the Moon and plans on doing the same to Earth in a year. Until then, he's going to fulfill a promise to be a teacher, and he's going to do it perfectly. As such, based on what we know, the only reason people targeting him can be considered bad guys is because they don't always care about not putting Class 3-E in danger. Ultimately, he proves himself Good All Along, when it was revealed that he actually didn't destroy the Moon (it was a lab rat), but he took the blame anyway, while teaching Class 3-E was him fulfilling his promise to the dying Aguri, and he actually wants to be killed before the antimatter cells inside his body destroy the world.
- Was Once a Man: He originally was a fearsome assassin known as the Reaper, until some government experiments turned him into what he is now.
- Wax On, Wax Off: An odd variation, in that he applies much more dangerous training for a much more mundane purpose. He's not only training his students to be cutthroat, speedy killers, but he's also helping them grow into fully functioning adults. Sometimes, he applies both at the same time, giving advice that applies for both assassination and life in general. Even in Episode 32, where he directly advertises the school festival as being entirely unrelated to assassination, the students still think of the two as similar, with Terasaka even calling Koro-Sensei's idea an "assassination restaurant." It ends up going a bit too far for Nagisa, who gets the idea of becoming directly applying his assassination knowledge when he grows up by becoming a professional assassin.
- Weaksauce Weakness:
- Weak to water. Specifically, his body is sponge-like. Even a day with high humidity causes him to swell up comically. If he actually found himself immersed in water it would certainly get much worse and slow him down significantly. The mucus his skin releases can protect him from it, but it can be depleted.
- The anti-sensei weapons are basically his Kryptonite, which is notable as it's completely harmless to normal humans.
- What Could Have Been: In-Universe, Aguri thinks that had he not grown up in a Wretched Hive, most of his personality quirks or weaknesses (other than his inability to swim) would've likely been expressed as a human being as well.
- Why Am I Ticking?: The real reason he will destroy Earth on March 13 is because the antimatter-generating cells Shiro/Yanagisawa put in his body will make him explode.
- Willfully Weak: He asked his tentacles to make him weak, so he could become a teacher that could easily get along with others and protect his students.
- World's Best Warrior: He held that title alongside his disciple as the greatest assassin. After the transformation, he became the World's Strongest Man, but he wanted to be killed by his students.
- Your Days Are Numbered: He is going to die in upcoming March 13 anyway, since his anti-matter generating cells will make him explode. Actually averted, in that the chance of instability and thus antimatter explosion decreases with increasing body size. For Koro-sensei, who is at least twice as large as a fully-grown human, the odds were ridiculously small to begin with, but drinking a certain chemical mix would reduce the chances to less than 1% (and that was the very formula that made his body as liquid way back in the beginning chapters of the series). Unfortunately, when it comes to a true Global Extinction Event, the only acceptable probability is "zero".
