Itona Horibe

Itona Horibe is the second assassin transfer student to arrive at Class 3-E, following the previous assassin, Ritsu. In his initial appearances, he didn't attend classes, but did reappear in a few chapters throughout the series until ultimately joining Class E for good.

Appearance
Itona has short, spiked platinum blond hair (light blue-tinted white in the anime) which as of Chapter 87 he now wears a large bandanna over and sharp light blue eyes (yellow in the anime).

Personality
Originally, Itona had a deep hatred of losing and being weak. He sought to kill Korosensei and prove he was the strongest because of this. He is also brutally honest.

After being abandoned by Shiro and befriending Terasaka and his gang, Itona has cooled down, but still retains his brutal honesty. Thanks to Terasaka's words of encouragement as well as Class E's admiration of his abilities, his desire to kill Korosensei has become less self-centered and is now willing to work together with Class E to attain his goal. Because of this, he has become much more sociable and involved with his fellow classmates.

History
Itona is the son of Horibe Electronics Factory's former president. After his father's company went bankrupt, Itona was abandoned by him which became a source of bullying towards him as well. One night, he was found by Shiro who told him that in his eye lies a tenacity for power and that he would help him achieve that power in order to grasp victory.

Plot
Itona makes his debut in Chapter 29 as the second transfer student to Class 3-E. Upon his entrance, he walks through the back wall of the classroom (with the class exclaiming to him to use the door) and states that he is victorious and has proven himself stronger than the classroom walls. The class states that another pain has turned up and Korosensei has an odd and unreadable expression on his face. Shiro introduces him and tells Korosensei that he'll be watching over Itona for time being since he's spoiled him a bit. While Nagisa notes that two have probably had more than their fair share of problems, Karma asks Itona why he's dry when it's pouring outside and he wasn't carrying anything. Itona starts glancing around the room until his eyes fall on Karma. He starts telling him that he's probably the strongest in the class, but he's weaker than him so he won't kill him. He then gets up and states that he only wants to kill those who might be stronger than him and in the classroom that only means Korosensei. In response Korosensei asks Itona if his talk of "strong" and "weak" refer only to fighting and that in a contest of strength he wouldn't be able to stand in the same dimension as him. Itona says that he can because they are brothers related by blood, shocking the rest of the class and even Korosensei himself.

After stating that, Itona tells Korosensei that as siblings there is no need for petty tricks and that he will kill him and validate his strength. He sets up the time for it for after school in the classroom and tells Korosensei that that would be his final class and to say his farewells to the other students. He then exits through the hole he made in the wall. Later, the students of Class E are noting the similarities between the new transfer student and their teacher like how they both have a sweet tooth and how they both look at gravure magazines. The latter provokes Okajima to state that he sees them in a more realistic light and that they are all brothers when it comes to liking big chests on women. Kayano asks why Korosensei doesn't know abut him if they are brothers and Fuwa begins to let her imagination run wild with a story about prince brothers separated due to a war. While Kayano and Hara are trying to make sense of her story, Nagisa glances at Itona who briefly glances back before returning to his magazine.

The school day continues and it's now the final bell, thus the time of the match. The classroom has been turned into a fighting rink of desks. Shiro makes one rule for the match and that is if Korosensei takes one step out of the rink then he'll be executed on the spot. By doing this, he's given Korosensei no place to run because if he breaks a rule that is decided in front of everyone then it'll ruin his credibility as a teacher. Korosensei agrees to that lays out the condition that harming the students watching will also mean defeat which is agreed to. Shiro calls the signal and upon it Itona lops off Korosensei's arms and in the process reveals that his hair doubles as tentacles. This answers Karma's earlier question of how he remained dry in the rain despite having nothing with him. Korosensei's face becomes black as he grows with anger, asking where Itona got those tentacles, surprising him. Shiro responds by saying they have no obligations to tell him and that despite the fact that Itona has a different background and parents, they are indeed brothers. He then proceeds to taunt him by asking if those tentacles bring to mind something unpleasant which it does.

Korosensei says that he needs to ask some questions as well and Shiro responds by saying that he won't as he will be dead then proceeds shine a beam on Korosensei which makes his body go rigid. Itona then proceeds to relentlessly and mercilessly attack Korosensei with his tentacles. While it seems he's got him cornered it was revealed that his "brother" managed to narrowly escape by using his molting technique. Shiro pointed out that molting and regeneration drained his stamina considerably. Itona continues to attack relentlessly with his tentacles with Korosensei barely keeping up his speed to block them. Shiro then shines the beam and with Korosensei gone rigid, Itona lops off some more tentacles gradually making Korosensei weaker and will soon kill him. The students of Class E see just how this bothers them and Korosensei begins noting that the "assassination" was actually a meticulously calculated plan and that if he wishes for answers, he'll have to win the match. Shiro taunts him and he says that there was one more thing he forgot to take into account which was his main weakness: the Anti-Sensei Weapons and that if his tentacles are truly the same as his, then they would share this weakness. Korosensei the proceeds to trap Itona in the skin he molted and throws him out of the rink, giving him the win. This deeply angers Itona, causing his tentacles to turn black and he begins to attack only to be stopped by Shiro, who shot him with a tranquilizer dart. He picks him up and begins to leave stating that Itona will be allowed to return to school soon enough.

Abilities
Mechanics and Engineering: Itona has knack for gadgets and tinkering due to learning the basics of mechanical and technical engineering from his father's company. He often puts his skills to good use with not just assassinations, but also in spying and reconnaissance when needed. He is often tasked with using custom-made RC vehicles that he constructs for reconnaissance.

Intelligence: Itona was revealed to have a high level of intelligence that was hindered and couldn't be used due to his tentacles.

Other Skills: Itona has incredible physical abilities that he possibly retained from his modification with Shiro. This was shown during the climax of the Athletic Festival Arc when he performed a six foot jump into the air after being catapulted by Isogai (the average vertical jump for a 14-15 year old male is about 17 inches) and brought Class A's pole to the ground.

Shiro
Itona's former caretaker who found him one night after his father abandoned him. Shiro promised Itona the means for victory and power and with his technology, modified and equipped Itona with tentacles. Later, in the Itona arc, Shiro abandoned him thus ending any form of relations.

Ryōma Terasaka
Terasaka is the person who managed to open Itona's heart and convinced him to change his ways. After Itona reforms and officially joins Class E, he is in Terasaka's group and although he doesn't miss a moment to call Terasaka an idiot or stupid, the two are good friends.

Quotes

 * (To Class 3-E male students, Chapter 88) "It's okay if I fail 100 times, I'll kill him for sure in the end. You'll help me out, right guys?"

Trivia

 * Itona's favorite subject is Science while his least favorite is Social Science.
 * His hobby/special skill is working with electronics.
 * His treasure is a soldering iron that was used by his father.
 * His favorite food is Paitan Ramen.
 * He was called "Rolling Riser" during class 3-E training using code names.
 * When the tentacles asked him what he wanted, he answered, "I want to be strong."
 * While under the influence of the tentacles, he followed Korosensei in almost every way. He had Korosensei's: sweet tooth, interest in big boobs, opaque expression, and ate all the same snacks Korosensei had.