Korosensei

Korosensei is one of the two overarching protagonists (alongside Aguri Yukimura) of the manga/anime series Assassination Classroom. He is the homeroom teacher for Class 3-E of Kunugigaoka Junior High School.
Korosensei claimed to be responsible for destroying the moon and thus causing its permanent crescent shape. He claims he will destroy the earth after teaching Class 3-E for a year. Prior to being a teacher, he was the master assassin known as the God of Death or The Reaper until he was betrayed by his apprentice, and captured, then used in experiments that gave him a new appearance and powers.
While he was captive, the scientist Kotaro Yanigisawa did experiments on him with anti-matter tentacles. He was monitored by Aguri Yukimura, the original homeroom teacher of the Class 3-E of Kunugigaoka, with whom he falls in love with. When his attempt to escape the lab results in her death, Korosensei promises to use his new powers for good and honor her memory for the remaining year he has to live by becoming the new teacher of 3-E, in order to guide and watch over her students.
In Japanese, he is voiced by , who also voiced by Lelouch vi Britannia from the Code Geass series and Roy from the Fire Emblem franchise. He is voiced by Tomokazu Seki in the OVA and Masaya Onosaka in the VOMIC version of the show.
In English, he was voiced by in all anime appearances. 
==Appearance==
Korosensei used to be a human with small black eyes, short dark hair and pale skin. While working as an assassin, he would wear dark colored clothes, usually black or brown.
After being used in experiments, Korosensei acquired the appearance of a yellow bipedal octopus. He is about three meters tall and possesses a large, bulbous head with a large smile and small, beady eyes. He uses two feelers as arms, with two fingers each, and utilizes the rest of his tentacles to walk with. 
Korosensei also dons a black academic dress, a small black square academic cap with a yellow tassel, and a large black tie with a yellow crescent-shaped moon on it.
==Personality==
It was revealed that he was raised in an environment "where everybody could easily betray one another to the point that one could only trust oneself". Through these hardships, he decided to become an assassin in order to survive. Despite he gained an apprentice, he only saw him as a tool for his goals, which eventually caused the latter to betray his master.
However, after meeting to Aguri Yukimura, he finally knew what compassion really was becoming much kinder and more sympathetic. According to Aguri, 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.
When first introduced, Korosensei is an easygoing individual who demands absurd and seemingly mundane requests despite claiming he will be the cause of the planet's destruction in a year. He is also rather kind to others in general and can switch from silly and childish to serious on the fly. According to Nagisa, Korosensei also is unintentionally petty at others at times and loves gossip, both traits heavily noted through the series.
==Powers and Abilities==
Due to the human experiments of producing antimatter in a living body by Shiro, Korosensei's entire appearance is of an octopus-like creature with multiple tendrils that are his tentacles. Anything aside Anti-Sensei Weapons will be immune to him. It is initially believed that he will self-destruct by the time of Class E's graduation; however, it has since been proven that the chances are minuscule at best.
One of Koro-sensei's most advertised assets is how fast he is and that he can move around the world at velocities up to Mach 20 like he’s some kind of superhero. Koro-sensei's intense speed is also shown to have another purpose, which is used more for visual gags than an advantage in battle. Koro-sensei's speed can produce many after-image versions of himself, but rather than merely act as illusions, they can also carry out rudimentary tasks. It doesn't just confuse the opponent, but is a brilliant way to maximize limited time.
Even before Korosensei gained his powers, he possesses a gifted mind which allows him to learn and understand complex knowledge in a matter of minutes. With his immense intelligence, he was able to single-handedly teach all the subjects and produce amazing results from the bottom of the barrel class of 3-E. Since gaining his speed, Korosensei has become hypercognitive, and can process information thousands of times faster than the average human being. His incredible mentality combined with his speed also allows him to multitask on up to dozens of jobs at a time (teaching the entirety of Class 3-E individually and then some), all of which seemingly being done simultaneously. Most impressively, he was able to give the assassination AI Ritsu approximately 985 upgrades in less than a single day, completely transforming her, increasing her intellect, and giving her personality and sentience.
==In other media==
===J-Stars Victory VS===
Korosensei is notably the only character from Assassination Classroom to appear as one of the playable characters in the anime crossover fighting video game J-Stars Victory VS.
===Weekly Shōnen Jump Jikkyou Janjan Stadium===
Korosensei appears as one of the playable characters in Weekly Shōnen Jump Jikkyou Janjan Stadium, a free anime crossover fighting mobile game for Android and iOS developed by Konami.
==Quotes==
==Trivia==
*His name, Korosensei, is a combination of the words 殺せない (koro, 殺せない) which means "unkillable" and the word 先生 (sensei, 先生) which means teacher. This name was given to him by Kaede Kayano, both in the original and in the RPG spinoff Koro-Sensei Q!
*Korosensei was called "Stupid Chicken Pervert Octopus" during class 3-E training using code names, rather than the code name he suggested, 'the imperial prince of fate of the eternal wind'.
*It is revealed that Korosensei has never actually known his real name.
*Korosensei is usually represented by an octopus due to his appearance of his head and tentacles. He is aware of it as he often draws octopus figures while scoring exams and chooses to be an octopus in video games.
**He also has a nature similar to octopus, as he is highly intelligent for his survival skills.
**His ability to regenerate his tentacles, healing others, bestowing wisdom, and octopi appearance is a reminiscent of the .
*In the popularity poll in Volume 12, Korosensei was ranked 3rd.
* Korosensei is ambidextrous, being able to write/perform a task with either hand, and being able to work with both hands at the same time.
*His motto is "Learning and killing are of one body."
*According to Aguri, Korosensei is not Japanese.
*One of Korosensei's weaknesses is large breasts. He owns a lot of erotica and pornography magazines and is easily distracted by breasts.
*When his tentacles asked him what he wanted, Korosensei's response was: "I want... to be weak".
*His necktie is a present from Aguri Yukimura. Though, the crescent moon motif is his own design.
*In chapter 136, he disguised as a university professor.
*Korosensei is portrayed by Jun Fukuyama, who previously portrayed another manipulative protagonist, Lelouch vi Britannia's from Code Geass series.
*He also is one of the most popular and recognizable Anime Heroes, in addition to being one of the primary members of the Shōnen Jump characters. The reason why he is notably the only character from Assassination Classroom to become one of them is mainly because of some of his anime references that he has done.
*Many of Korosensei's weaknesses are meant to be ironic. Some examples are that he has motion sickness even though he can move at Mach 20, can't swim or get wet, and sucks at reporting despite having the time to change clothes, make tea, and build a large sandcastle in half a minute, which are all ironic.
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