Name: Real name unknown, Nick-named "Korosensei" by Kaede Kayano, Code-named "The Reaper"

Origin: Assassination Classroom

Height: ~7'6½"

Weight: N/A

Gender: Male

Age: Unknown

Classification: Artificially Modified Human, Assassin, Teacher

Theme: 

https://youtu.be/2yIP6LQ_yiY

FEATS:

-As The Reaper, managed to breach the security of the leader of a superpower and make it appear like a natural death and ended a ten-year civil war by killing two dozen military officers in a week

-Easily bested almost all of the assassins that attempted to take his life

-Successfully greatly improved the grades of the entirety of Class 3-E

-Installed over nine hundred upgrades on Ritsu on his own

-Bested Itona in their first battle through experience and wit alone

-Saved both Itona and Kayano from the tentacles

-Managed to remove a tumor from a woman's brain, healing her blindness in the process

-Caught almost every single cell from Kayano's fatal injury while fighting Reaper 2.0, later using them to perform a full surgery

-Memorized every problem set that has ever existed in Japan in order to teach his students

Monika: Class 3-E of the Kunugigaoka Junior High School, a class made entirely to segregate the "weakest" students from the school as a whole, was one of the worst positions to be in for any student.

Junko: But everything changed when the Fire Nation attacked!

Monika: Or um when 70% of the moon blew up and a strange 7-foot-tall tentacle monster threatened to do the same to the earth unless he became their teacher and they successfully killed him before they graduated.

Junko: I'm sorry, what?

Monika: Let's... back up a little bit. So before he was a 7-foot-tall tentacle man, he was a nameless masterful assassin known only as The Reaper for his incredible skill in the field. During one of his missions, he had accidentally allowed his target's child to witness the kill, which left the boy desiring to become a killer, just like his father's assassin. Taking the boy in as an apprentice, The Reaper taught him everything he knew without ever truly caring for him as a student, seeing the boy merely as a tool to obtain more opportunities for assassination.

Junko: Yeah, because that's never bit anyone in the ass before.

Monika: Right, this methodology eventually led The Reaper to his downfall, being betrayed by his student and captured to be experimented on by a scientist known as Kotaro Yanagisawa, who was attempting to create organic antimatter, using The Reaper's body as a guinea pig. But as his body was constantly experimented on, The Reaper ended up forming the first true bond of his life, a lab assistant and teacher of Class 3-E named Aguri Yukimura. By talking to her and finally opening up about his past, The Reaper finally started to grow as a person, learning about compassion and what it truly meant to be a teacher.

Junko: Wait... Human experiments finding love in someone who was a part of one of the greatest schools in the country before their experimentation causes them to look drastically different than who they originally were? Something about this feels... familiar...

Monika: Well, tragedy striking was pretty much inevitable. Remember that moon explosion? That wasn't Korosensei's doing. Rather, a test to see what would happen with the antimatter in The Reaper's body at the end of his lifespan, a lab rat was sent to the Moon at the end of its own lifespan and exploded... which destroyed 70% of the moon. Calculating that the same destructive event would happen to The Reaper within a year, the scientist prepared to kill him immediately to prevent the destruction of Earth. But Aguri, having learned of what was about to happen to The Reaper, told him about this, and so he used the powers he obtained from the experiments to break free. But as Yanagisawa and his men attempted to stop the rampage of the empowered assassin, Aguri ended up a victim of a weapon meant to eliminate the Reaper. In her dying words, she still believed in The Reaper's potential as a teacher, asking him to take her place and teach Class 3-E.

Junko: So this guy's basically an extroverted version of Izuru Kamakura. Got it.

Monika:  Keeping his identity as The Reaper a secret, he would become the teacher of Class 3-E. And due to him being near unkillable, the students will name him Korosensei, quite literally meaning... the unkillable teacher.

https://youtu.be/BGTYGVpYsas

Junko: Korosensei is incredibly strong! He's lifted large, iron beams and dropped them off in two locations across the planet, and has even created a tornado strong enough to spin clouds! He's crashed into mountains, caught and carried large missiles casually, and broke out of an Anti-sensei cage that not even tanks could destroy!

Monika: He should be comparable to the Reaper 2.0, who can pulverize a 30-story building and create fairly large craters in the ground. Korosensei himself leveled an entire facility mere moments after obtaining his antimatter.

Junko: He's durable enough to let himself get hit by multiple guns with 470 rounds of ammunition just to trick Miss Yellow Bitch. He can take hits from Itona's tentacles and even managed to hold on to Kayano long enough for her to be incapacitated while her tentacles were stabbing his heart!

Monika: Kayano's tentacles were strong enough to create massive holes in the ground. But Korosensei is more known for his Mach 20 speed.

Junko: The guys dodged simultaneous gunfire from his class while taking attendance, casually lew from Japan to America in order to watch a baseball game, and even flew across the planet fast enough to create contrails in the shape of his face.

Monika: He once performed a full-body deep tissue Swedish spa-level oil massage on Irina before changing her into old gym clothes, all in a single minute. And he's read a year's worth of Saikyo Jump manga, then found, bought, and read a year's worth of its rival magazine all in one second. He even managed to avoid the light-speed Spear of Heaven laser with only minor injuries, though considering the fact that he sensed it beforehand and the laser was fired from 400 kilometers away, he wouldn't need to match its speed to do so.

Junko: Right. Still, now is probably the time to note that Korosensei is super smart.

Junko: I mean, during his time as the Reaper he obtained so many skills that it was believed that the only way to defeat him at all was to be better than him in every single way possible!

Monika: It was these skills which he would eventually pass down to his apprentice, and later to the students of Class 3-E. He also has several specific skills which come in handy for assassin work. Like the Clap Stunner, a technique in which Korosensei creates a specific type of sound in order to stun an opponent and incapacitate them. Normally, this technique has several conditions to be used, but Korosensei's skill is so great that he can do it simply by yelling loud enough, or striking a surface in a certain way.

Junko: Or the Invisible Sythe, where he fires a minuscule projectile to pierce the gap between muscle and bone, utilizing his knowledge of the human body in order to incur excessive bleeding. He could even do this with a projectile as mundane as a grain of sand, and was so skilled with this technique that it was considered his secret weapon!

Monika: Then there's his human reading.

Junko: Which is pretty much as it says. Korosensei possesses a great aptitude for reading the facial expressions and body language of people, allowing him to discern their intentions, or whether or not they are lying. This is beneficial in combat since it lets him determine what a target is about to do next pretty easily. Korosensei possesses immense skill and experience in combat due to his time as The Reaper. Since he's the world's best assassin, he naturally proved capable of avoiding or countering nearly any assassination attempt that his students attempted, even those from professional assassins. He's even shown to be capable of defeating enemies who are even stronger and faster than he is, such as Reaper 2.0. Throughout his time as an octopus man, he developed a number of new abilities and improved in combat even beyond where he already was, demonstrating himself to be a genius fighter.

Monika: He's a genius outside of combat too. He has extensive knowledge of every topic taught in schools, to the point of being able to instruct all of his students simultaneously by dedicating an afterimage to each one of them. He is also capable of reading an entire year's worth of manga almost instantly and creating inventions more complex than what is possible with contemporary science. He was also able to upgrade his A.I. student, Ritsu, adding 985 modifications within a single day.

Junko: All this thanks to some scientific enhancements?

Monika: Well... no. This more has to do with his eidetic memory, which refers to the ability to recall an image from memory with high precision after seeing it only once. This is distinct from a photographic memory in that it specifically refers to the ability to recall images, sounds, and other sensory aspects, while photographic memory pertains to things like text and numbers. Interestingly, however, Korosensei seems to be capable of the latter as well, as he was able to memorize every problem set that has ever existed in Japan for teaching purposes. Being able to draw upon everything that he has learned was a large part of what allowed Korosensei to become the world's greatest assassin.

Junko: So his intelligence is a human thing, but the rest of him definitely isn't.

Monika: Right, his body was completely altered by the antimatter experiments, turning into a being with an octopus-like appearance and several tentacles. Due to this, no traditional weapon is effective in harming Korosensei, melting the moment they make contact with his body. Other functions of these tentacles are giving Korosensei the ability to camouflage himself like a chameleon and giving him a tongue that can melt through any substance, including Anti-Sensei materials that are normally effective tools for harming him.

Junko: And he's got a healing factor.

Monika: Should any of his tentacles receive any damage or be severed, Korosensei is able to regenerate them completely. This does come at the cost of lowering his stamina, however. His regeneration is even potent enough to regenerate his own heart after having been stabbed through it.

Junko: He can also shed his skin, which will completely regenerate his body from any harm done, and his molted skin can be used as a protective substance to either immobilize his opponents or protect himself. Though this causes him to lose a bit of stamina too and become slower until he's rejuvenated.

Monika: Korosensei is also extremely resistant to poisons. When one of his students gave him several harmful concoctions to drink, they only managed to cause random effects on his body. Certain chemicals also have specific beneficial effects, such as granting him a liquefaction ability, or decreasing the likelihood of his antimatter self-destruct activating to less than 1%. 

Junko: It also granted him a weird liquid form.

Monika: After tricking Manami Okuda into making him a specific chemical concoction, Korosensei gained the ability to turn his body into a liquid state, allowing him to fit into tighter spaces and as such, making him even harder to hit. He has showcased the ability to turn into this state later on, proving that the effect of the concoction was permanent.

Junko: He's got other forms too like his Ultimate Defense form.

Monika: A form created by compressing himself into a small ball surrounded by crystalline armor. In this form, it is established that not even a nuclear warhead would be able to scratch him. However, after a day, it'll slowly dissipate and he'll return to his usual form. All previous damage done to his body will be completely restored and his energy will be rejuvenated. The main drawback of this ability is the fact that it renders him immobile, and he cannot deactivate it at will. According to Korosensei himself, it would be possible to defeat him in this form by launching him into space while he is defenseless, but it would be impossible for humanity to do that within the 24 hours that he remains in the form. It's also not completely indestructible, as it is established that a laser made of antimatter particles could have destroyed it.

Junko: Yeah, Korosensei's body is weird. I mean, he can stretch his tentacles long enough to make a net to catch Karma!

Monika: He did this in seconds while Karma was already falling, and the web is shown to be sticky, immobilizing Karma as though he was caught in a spider web.

Junko: Wait, was it sticky cause of his mucus? 

Monika: I sure hope not... but his natural mucus comes with a handful of uses, despite the nastiness of it all. The mucus is durable enough to stop bullets dead in their tracks and can be used stealthily by making his Mach 20 movement speed nearly completely silent. It has some non-combat uses as well, such as being handy for massages and capable of creating bath foam that can eliminate dirt. He can even use it to help repair gaps on a cellular level. In addition, the mucus can also prevent Korosensei's body from sucking up water and having his mobility hindered, adjusting the osmotic pressure by mixing it up with the water around him.

Junko: He can also somehow generate electricity.

Monika: This would involve sending an electrical signal through the heart in order to correct arrhythmia. 

Junko: Theoretically speaking, this could also do the opposite, interfering with the electrical signals in the heart in order to disrupt or stop the heart of a living target.

Monika: Back on his speed he has what we'll call a Mach Whisper.

Monika: He can whisper in order to implant thoughts and copy the monologues of those around him, and then leave at Mach speed before anyone notices his antics. This allows him to influence the thoughts and actions of other people to a limited extent.

Junko: Please, that's just ridiculous. How can he ever [notice how beautiful Monika is. I should marry her.]... Hey, wait a sec!

Monika: What? I don't know what you're talking about. I didn't do anything.

Junko: Hmm...

Monika: Anyway, let's talk about Korosensei's face!

Junko: Oh yeah, is it always like that?

Monika: Well, no...

Monika: Korosensei's body is usually yellow, but whenever he feels certain emotions, his color will change accordingly. While mostly used for the sake of visual gags, it was revealed during the final battle against the Reaper that when the body of a tentacle being turns pitch-black, it represents them losing control over their emotions and allows them to use the fullest extent of their power. 

Junko: At least that is until Korosensei used these colorful emotions, bottled them all up, and blasted them away in the form of a literal laser beam!

Monika: The final ability that Korosensei developed before his death at the end of the series, this technique allows him to, as the name suggests, shoot laser beams. As it's tied to his emotions, it's usually fairly weak, but after combining all of his colors into the laser and turning it white, he was able to make it much more powerful. At its strongest, it was great enough to one-shot Reaper 2.0, who was stated and shown to be much more powerful than Korosensei himself.

Junko: But even with him firing Kamehameha Waves or catching military missiles as souvenirs, Korosensei still has his own weaknesses.

Junko: I mean he has a ton of weaknesses that can slow him down. Like how he's quick to panic, is petty, has soft punches, gets motion sickness, likes to gossip, can't swim, is tone deaf, can't handle spicy food, sucks at reporting, can't draw anything other than simple cartoons, sucks at hiding, can't sleep with pillows outside of his own, is a pervert... the list goes on.

Monika: The only really important weaknesses he has are his lack of brute strength, which makes him heavily rely on his speed in order to escape assassination attempts. His regenerative abilities take a considerable amount of stamina to use, which can slow him down considerably, and if his heart is completely destroyed, he will most certainly die.

Junko: His reliance on speed has other drawbacks, especially when it drops to human level if he's surprised. Anti-Sensei Weapons like the ones typically used by Class 3-E can easily destroy his unique body if they make contact with it.

Monika: But his biggest weakness is his students, as he will always put the lives of Class 3-E over his own, being willing to go through any risk in order to save them if they ever find themselves in any sort of danger.

Junko: Because nothing matters more to him than his student's success!

Korosensei: So long as I have time... I will use this as a teacher. The students you watch over, I will watch them myself. No matter what, these tentacles will not let them go.