Koro Sensei !!

Korosensei has the appearance of a yellow octopus who is about three meters tall and possessed a large, bulbous head with a large smile that rarely breaks or moves, and small, beady eyes. He uses two tentacles as arms, each having two feelers as fingers, and utilized the rest of seemingly jelly-like limbs - his tentacles - to walk. Korosensei has a pair of hidden nostrils, which make him appear to have four eyes if detected. Due to his constant grinning, he changes his color to express his emotions. Korosensei wears a black academic dress, a small black squarish mortarboard cap with a yellow tassel and a large black tie with a yellow crescent-shaped moon on it, a gift from Aguri Yukimura. As a human, he had pale skin, a slender build, dark eyes, and short black hair that reached to his nape. He sports an amicable smile, which was initially used to manipulate others. When carrying out assassinations, he donned formal clothing. After being taken prisoner by Kotaro Yanagisawa, he was put in patients' scrubs until his escape and transformation. 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 to survive. Despite gaining an apprentice, he only saw him as a tool for his goals, which drove the latter to finally betray his master. However, after meeting Aguri Yukimura, he finally knew what compassion really was--becoming much kinder as a result. According to Aguri, if he was born in a peaceful country, he would be "a little lecherous, smart, klutzy, kind of stingy and stubborn" and he would smile because he is genuinely a kind person.[3] This prediction happens to reflect his personality; which became forefront after he answered the tentacles. When first introduced, Korosensei was an upbeat individual who demanded absurd and seemingly mundane requests despite claiming he would be the cause of the planet's destruction in a year. He was also rather kind to others in general and could switch from silly and childish to serious on the fly. According to Nagisa Shiota, Korosensei also was unintentionally petty at others at times and loved gossip, both traits heavily noted throughout the series. From time to time pieces of his old personality as The Reaper were visible such as when Ryoma Terasaka tried to sacrifice Nagisa to kill Korosensei and Korosensei menacingly threatened all of their families if they tried another self-harming attempt like that. In that moment, he resorted to his old method of teaching through fear. As the series progresses, his character development renders him more and more capable of true empathy and learning to use that empathy to teach lessons instead of through fear and reward like he had with his first student. Korosensei deeply cared for his students' emotional and physical well-being and would lose his temper whenever any of them were put in danger, even by one another. On the annual school trip to Kyoto, a few of his students were assaulted/kidnapped by a gang of high schoolers hidden in an alley. After searching the entire area painstakingly, he infiltrated the abandoned building where two of his students, Yukiko Kanzaki and Kaede Kayano, were being held at and single-handedly beat up all of the high schoolers, scaring them away.[4] One of Korosensei's attributes was that he was able to connect to each student individually, being an objective, empathetic, and observant person who will do almost anything to help his students. This was why all the students respected him even though he would blow up the Earth in a year. Taking care of each student's needs, Korosensei would sometimes be piqued by a student's current problems or interests and would try his best to guide the student along or solve it for them. Korosensei loved sweets almost to extreme cases,[5] and was also shown to be a very perverted character, a trait he shares with his student Taiga Okajima and Itona Horibe. This characteristic was revealed to be the side effect of the experimentation with anti-matter tentacles which made him unable to hide his true feelings. Koro-sensei's name is a play on words. It is a portmanteau of the phrases 殺せない (korosenai, 殺せない), which means "unkillable", and 先生 (sensei, 先生), which means "teacher". It was given to him by Kaede Kayano.[6] HISTORY- As a child, he was born into one of the vilest and corrupt slums in an unknown country. He never knew his real name or his birthday. It was an environment where everybody could easily betray one another to the point that one could only trust oneself. Through these hardships, he learned that there are only three things you can really count on: skill, money and death. This ideology is what made him decide to become an assassin, eventually becoming the master assassin known as The Reaper after his one-thousandth kill. Those who were stronger than him, he killed with his intellect; those who were smarter, he killed with strength; those who were strong and smart, he killed with his charm. Immediately, his talents were shown as he left a tremendous trail of corpses in his wake. He became notorious for breaking through even the most strict security teams to assassinate his targets without any hitch. All this changed after assassinating a wealthy businessman and father. The man's child witnessed the killing and became enamored with the beauty of the kill, requesting that the Reaper train him as his apprentice. Eager for the assassination opportunities that an apprentice could give, the Reaper took in the boy and trained him. He taught him everything he knew, all while still instilling respect and fear in him and letting him know the difference in power between them, although he only saw him as his tool rather than a real student. After several successful jobs, the apprentice turned on The Reaper as he was attempting to escape a prison facility. The apprentice, later the current Reaper, sought his master's title and abandoned him just to fuel his ego. Betrayed, the Reaper was captured and thrown into an undocumented research laboratory run by Kotaro Yanagisawa. Yanagisawa's research goal was to create large amounts of organic antimatter by having it "piggyback" on the growth of human cells. It was there that he met and befriended Aguri Yukimura, a teacher who was in an arranged and abusive marriage to Yanagisawa at the time. She was brought in to keep a closer eye on him as Yanagisawa considered her easily expendable if he attempted to break free and take her hostage. As the tests continued, the Reaper began to slowly bond with her and became fond of her as she worked on compiling exam questions for her class, and it was during this time he learned what compassion was. One year after he had been imprisoned in the lab, Aguri got him a large tie as a present, since he would complain about his neck being cold and because he didn't know his actual birthday, she thought their anniversary was as good a day as any. However, a problem arose when Yanagisawa and his researchers questioned what would happen to Korosensei's antimatter cells when he died. To answer this question, Yanagisawa and his team launched a small automated lab onto the moon to safely test the possibility of what happened if a subject with Korosensei's antimatter-infused cells were to die, in this case, a small lab rat. When the rat did die at the end of its lifespan, it caused a volatile reaction with the antimatter in its body. The antimatter created a chain reaction that turned 70% of the moon's matter into antimatter, which completely exploded. Upon seeing this, Yanagisawa was horrified at the results. His subordinates then began running calculations and discovered that the same thing would happen to the Reaper by March 13 of the following year. Earth would be destroyed the same way if left unchecked, prompting Yanagisawa to order his subordinates to start preparations to kill him. A mortified Aguri overheard this and decided to go speak to the Reaper and tell him their findings. However, when she did, he revealed that it does not bother him as he expected a death such as this from the start. Telling Aguri to leave, he finally unleashes his full power that he gained from the experiments to escape as a visibly fuming Yanagisawa watches from a nearby security camera. The Reaper then proceeded to rampage violently, killing off several guards, destroying the building, and in the process of it all damaging Yanagisawa's left eye. However, during the escape, Aguri is mortally wounded when she landed in the line of fire of a special trip-mine meant for him, to the latter's horror. He then laments that if he hadn't wasted his skills on killing, he would know how to save her. Her final wish to him was to teach the students of Class 3-E, all while thinking of what a wonderful teacher he would be. Depressed but not broken, the Reaper vowed to help those children. He took the tie Aguri got him, left a note, left the facility for a nearby mountain and then used various items on the mountain to create a new set of clothes to suit his new role as a teacher. Although not responsible for destroying seventy percent of the moon, he took the blame and told the world's leaders that he would destroy the Earth as well in March of the following year and requests to become the homeroom teacher for Kunugigaoka Junior High School's Class 3-E. The world leaders accepted the deal, hoping it would give them a chance to assassinate him; however, they also added another condition: he would not harm the students.