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Twenty Assassination Classroom (Ansatsu Kyoushitsu) Facts About Korosensei

'Fact Fact no Mi' is a three-person team. We like to write articles about our interest that include manga, anime and k-pop in our free time.

Assassination Classroom: 3-E Class

Assassination Classroom: 3-E Class


Korosensei, one of the protagonists of the Assassination Classroom series, is the new teacher of the 3-E Class at Kunugigaoka Junior High School. He made his debut in the first chapter of the manga and in episode 1 of the anime.

With his inhuman speed and strength, he is trying to change the students who have lost their will to fight and pursue their dreams. By giving them a new goal, to assassinate him, Korosensei started his training where he not only strengthened them physically, but also mentally. He helped every student discover what they are actually good at and focused their training on that. Despite him being the students' assassination target, Korosensei has won over their hearts as a teacher.

In this article we will write about Korosensei's:

Personal traitsPast and relationshipsOther





Moon incident

Anime references



Voice Actor

Moods and emotions


Code Geass








Korosensei was the teacher of the E-class at Kunugigaoka Junior High School. One student, Kaede Kayano, named him Korosensei - from Korosenai (殺せない), which means "cannot be killed" and sensei (先生), which means teacher, so it could literally be translated as "unkillable teacher".

His real name remained unknown, but we do know that he was formerly known as an assassin under the name of "Grim Reaper".

Korosensei was also called "Stupid Chicken Pervert Octopus" by the students during training using code names, rather than the code name he himself suggested - "The imperial prince of fate of the eternal wind".

Korosensei in his human form.

Korosensei in his human form.


Korosensei has the appearance of a yellow bipedal octopus. He is made from anti-matter and is 280 cm tall. According to Korosensei himself, his nostrils are so small that it looks like he has four eyes.

Korosensei has excellent sensory perceptions and is able to detect even the smallest changes in temperature, light, sound, and smell. Even though he has no visible ears or nose, Korosensei is able to hear things no normal human can pick up on and detect the most minor of aromas, which has helped him evade a lot of assassination attempts.

Korosensei is especially talented in identifying people by their smell and certain materials (such as explosives and poisons). His eyes are also quite keen - he can keep track of objects going thousands of miles per hour without difficulty, as well as detect the slightest of movements that occur quicker than the blink of an eye.


The reason why Korosensei became an assassin in his childhood were the slums, in an unknown country, he was born in. That place, where you could trust no one except yourself, was the worst environment for a child. Through these hardships he decided to become an assassin and became famous for his talent to kill his target no matter how strict the security was. That's why some called him the "God of Death".

Also, according to Aguri Yukimura, he is not Japanese.

Korosensei as a child.

Korosensei as a child.


Korosensei is very smart to the point that he could teach almost every subject by himself. He seems to have an Eidetic memory, as he is able to store all that he has learned and use it to his advantage. Also, in order to become an educator to the E-class, Korosensei has memorized all of the test books in Japan so he could be able to teach his students where their weaknesses lie.

His motto is "Learning and killing are of one body."


Korosensei loves sweets almost to extreme cases, but he was also shown eating several inanimate objects such as knives or a bomb. He could even drink poisons normally dangerous and deadly to humans.

Korosensei is ambidextrous. He is able to perform a task with either hands, and to work with both hands at the same time.

He was also shown to be very perverted, which was revealed to be the side effect of the experimentation which made him unable to hide his true feelings.

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According to Aguri Yukimura, if he was born in a peaceful country, his personality would be "someone a little perverted, with a good head but a few screws loose, petty about small things, and also a lot stubborn... or something like that." He has/would have "a gentle smile not just for business, but because he is a gentle person himself." This prediction happens to reflect his personality which became forefront after he answered the tentacles.

Korosensei: human and monster form.

Korosensei: human and monster form.


Korosensei can change the colour of his face according to his emotions and mood:

  • Yelow - when he is happy or neutral
  • Yellow with green stripes - mockery, when he is looking down on someone
  • Orange with a red circle - for a correct answer
  • Purple with a dark red X - for a false answer
  • Pink - when he is sleepy or smitten
  • Purple - when he is shocked or in panic
  • Blue - when he is sad
  • Red - when he is annoyed
  • Black - when he is furious
  • Pure white - a mix of every emotion (poker face) or him being bored
  • Mild yellow - when he is confused
Korosensei's moods and emotions.

Korosensei's moods and emotions.


Korosensei has a few additional forms which were triggered after he drank the poison which was especially made for him by Manami Okuda, a student from E-class.

  • The first test tube caused Korosensei to grow horns around his head. The poison was made from sodium hydroxide, which is harmful to a normal person but not Korosensei.
  • The second test tube, made out of thallium acetate, caused Korosensei to grow wings at the back of his head.
  • The third test tube turned Korosensei's face to normal, with a straight poker face.

After drinking the last test tube, Korosensei offered Okuda to help her make a new poison which would be able to kill him. That specially made toxin increased the fluidity of Korosensei's cells, causing him to melt. That way he could fit into any crack.

Korosensei's first perverted moment.


Korosensei's only natural weakness is boobs. That was already noticeable when Aguri showed him her ogre themed thumb top, so she remarked him as a pervert.

Other than his natural weakness, Korosensei has other flaws (39 of them) which were noted down by Nagisa Shiota during the entire time Korosensei has been their teacher. In Japanese, the number "39" is pronounced as "san kyuu" which sounds like "thank you".


1. Boobs (natural weaknesses)

21. Heat fatigue

2. When he tries to act cool, his weaknesses show

22. He's strict about poolside manner

3. He is surprisingly quick to panic

23. He can't swim

4. He is petty

24. He likes to gossip

5. His punches are weak

25. He is weak against the occult

6. He is humble and subservient to his superiors

26. If he can't gather people he feels worthless

7. He has no patience for wire puzzles

27. Tone-deafness

8. He gets motion sickness

28. He sucks at hiding

9. He can't sleep on a pillow other than his own

29. Gets carried away by official positions

10. He worries about appearances

30. Heart

11. He can't handle hot food

31. Acts like a doting parent

12. Getting wet

32. Gets insurance to avoid getting hurt

13. Juicy gossip

33. He doesn't really know what "your own football" means

14. Hackneyed plot developments make him cry

34. He sucks at reporting

15. He gets taken in by rumors

35. He suffers from road rage

16. Time right after molting

36. Restructuring

17. Time right after regeneration

37. Grabbing all his tentacles at once makes him unable to move

18. His body goes rigid when bathed in a special beam of light

38. Unintentionally adding insult to injury

19. When he returns to normal after a serious situation, he gets embarrassed

39. Completely oblivious to the mood in moments of high tension

20. He can only draw simple pictures

40. Class 3-E students - undeniably Korosensei's greatest weakness

Korosensei's weakness for boobs.

Korosensei's weakness for boobs.


Although the students of the E-class are subtly aware of his last weakness (No. 40), only three students ever made actual attempts to exploit this factor: Karma Akabane, Nagisa Shiota (both using themselves as baits), and Ryoma Terasaka (using Nagisa as a suicide bomber the first time, second unknowingly manipulated by Shiro into nearly drowning his classmates, but has redeemed himself since).

Also, when Korosensei's tentacles asked him what he wants in life, Korosensei answered that he wants to be weak.


Korosensei was hiding certain things from his students, which were revealed in Assassination Classroom Extras featuring Hotaru as main character of the series.

Here is a list of some foibles that he has as an adult:

  • Painfully narcissistic designs
  • His room resembles a dumpster
  • Kind of like an old geezer
  • Really can't hold his liquor
  • Takes forever to decide on an appetizer
  • Starts a night off with Orange and Cassis
  • A bit of degenerate octopus
  • His purpose has shifted from using porn magazines to collecting them
  • He only makes petty wagers
Korosensei's porn magazine collection.

Korosensei's porn magazine collection.


It is well known that fans enjoy mixing anime characters together and comparing them. When the One Punch Man anime came out, one of the most popular subjects was the question of who would win in a fight between Korosensei and Saitama. Though it is impossible to know which one of them is actually stronger, the fans still like to discuss this theme.

Another frequently asked question is who is faster, Korosensei or Saitama. After a long period of time, it was finally revealed. Due to the calculation done by one of the fans, it was determined that Saitama was faster.

They used the information that Saitama was able to go from the Moon back to the Earth in a short amount of time (roughly 10 seconds), while it takes Korosensei longer to fly even to some different country. Which would mean that Saitama has the upper hand when it comes to speed.


Assassination Classroom made a few references to some other popular anime including One Piece, Naruto, Gintama, Dragon Ball, Hunter x Hunter, Saint Seiya, Attack on Titan, Kuroko no Basket, Switch Girl and Saiki Kusuo no Psi Nan.

You can see Korosensei using clothes (doing cosplay) of characters from different anime (Luffy's straw hat, Gintoki's silver hair and his white yukata with a blue swirl pattern on the bottom, the Headband with the sign of Konoha...) in order to motivate and help his students with the preparation for the upcoming exams. He used some trade mark moves, like stretching his tentacles and imitating Monkey D. Luffy's famous move Gomu Gomu No Slingshot. There is also one scene where Karma is playing an One Piece game.


In Ansatsu Kyoushitsu chapter 138 it was shown that Korosensei didn't destroy the moon, it was due to a rat exploding.

People had made a laboratory on the surface of the moon, which they made a home of a rat. They had infused the rat with anti-matter for the purpose of investigating a way to single-handedly supply energy for an entire country. As a precaution the experiment took place on the moon, where there would be no casualties, but the results proved to be catastrophic.

Korosensei decided to teach the class to fulfill a promise to Aguri Yukimura (the former teacher of E-class), and made up the story that he destroyed the moon and the whole assassination thing, just so he would be allowed to teach.

Assassination Classroom: how the Moon was destroyed.

Assassination Classroom: how the Moon was destroyed.


After the 1st Grim Reaper assassinated a wealthy businessman, that man's child, having witnessed the killing, became captivated with the beauty of assassinating and requested that the God of Death trains him as an apprentice. The Grim Reaper taught the boy everything he knew. Later, the boy betrayed the God of Death while they were escaping a prison facility. The apprentice, now the 2nd God of Death, took his master's title and abandoned him just to fuel his ego.

After finally freeing himself, the God of Death proceeded to rampage in the laboratoruy, killing off several guards and in the process damaging Yanagisawa's left eye. However, during the escape Aguri was mortally wounded when she protected the Grim Reaper from a special trip-mine meant for him.

Korosensei and his apprentice Shinigami.

Korosensei and his apprentice Shinigami.


Korosensei's necktie is a gift from Aguri Yukimura. She gave it to him as she was dying, but the crescent moon motif is his own design.

He was unable to save Aguri due to his lack of ability in the new monster form, but he was able to save Miss Azusa from brain tumor and later Akari (Kayano Kaede) after he manage to defeat 2nd "God of Death" and Yanagisawa. He managed to do this because he learned a new technique - surgery, using his "other" tentacles. This new power was the consequence of Korosensei's failed attempt to save Aguri. Therefore he studied about medical operation and surgery methods.


At one point it was said that Korosensei would die in March, whether the students assassinate him or not. To find everything out about this data, Nagisa and Karma infiltrated the space station and upon inspecting the data, they found out that the chances of Korosensei exploding at the end of March were less than 1%.

Korosensei's death.


Korosensei was executed by Nagisa Shiota, one minute before midnight and before Lance of Heaven fired again. After turning into shining particles of light and disappearing into nothingness, Korosensei left only the clothes and graduation cap that he always wore.

Korosensei's death is somewhat similar to Lelouch vi Britannia's from Code Geass. They were both killed by their dearest friends in the last episode and requested by themselves to save the world. Also, both characters are voiced by the same japanese voice actor, Jun Fukuyama.

Lelouch as Korosensei.

Lelouch as Korosensei.


Korosensei's japanese voice actor is Jun Fukuyama, who also voiced Okumura Yukio from Ao no Exorcist, Lelouch from Code Geass, Kishitani Shinra from Durarara, Yata Misaki from K, Grell Sutcliff from Kuroshitsuji, Cassim from Magi, King from Nanatsu no Taizai, Kazuma from Noragami...

Nagisa becoming a teacher like Korosensei.

Nagisa becoming a teacher like Korosensei.


Seven years after Korosensei was assassinated, some of the former E-class students reunited to keep the old classroom building in tact. None of them had considered the necessity to build a gravestone for both Korosensei and Aguri, believing that doing so will reinforce the fact that they are both truly gone. Therefore, they consider the classroom building as their grave, due to the wonderful memories and experience they gained there.

His final legacy, however, was a student he considered his favourite: Nagisa becoming an educator himself, using a fraction of his tact for assassination to coerce his new rowdy and rebellious high school classroom into submission.

Korosensei and Aguri Yukimura's grave.

Korosensei and Aguri Yukimura's grave.

About Assassination Classroom series.

A mysterious creature destroyed part of the Moon and threatened to do the same with the Earth. He gave the government the chance to kill him before that happens, but under one condition: that he is to be a teacher to the E-class at Kunugigaoka Junior High School. The E-class has thus been assigned with the task of assassinating that monster, who is able to move at an incredible speed, up to Mach 20, and is unaffected by any weapon. That class consists of the "dumbest" students (those who had the lowest grades or worst behavior), who are considered to have no future. Will the E-class be able to assassinate the monster, Korosensei, despite the fact that they grew fond of him?

The main protagonists of this series are the inhuman teacher Korosensei, as well as the whole 3-E Class, especially Nagisa Shiota, Akabane Karma and Kayano Kaede. While going through a whole year of trial-and-error, they will slowly change themselves and regain their confidence to once again pursue their dreams.

© 2016 Fact Fact no Mi


Fact Fact no Mi (author) from Novi Sad, Serbia on July 10, 2018:

Interesting catch! Thank you for pointing that out :D

Kalastar on July 10, 2018:

There are also interesting references not related to any anime. In 2nd season ep. 21 there is reference to certain "religion", Pastafarianism. When Koro sensei is taking pictures for his yearbook there's picture called History of religion. On this picture we can see Koro sensei demonstrating Flying Spaghetti monster, which is worshipped by pastafarians.

FallenUzumaki on September 15, 2016:

Your forgot the Toriko reference

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