Itona Horibe

"I might fail a hundred times, but I'll be sure to kill him before it's all said and done. You've got my back, right guys?"

- Itona to his male classmates

Itona Horibe (堀部) is the second assassin transfer student to arrive at Class 3-E, following the previous assassin, Ritsu. He initially served as the secondary antagonist, before ultimately joining Class E for good.

Appearance
Itona has short, spiked platinum blond hair (light blue-tinted white in the anime) which he later wears a large bandana over and sharp light blue eyes (yellow/amber in the anime). Although fairly short, he possesses a strong build.

Personality
Originally, Itona had developed a hunger for strength from abandonment and being bullied, and thus hated the idea of losing or any position which made him weak. As such, he allowed Shiro to implant him with tentacles and became obsessed with killing the powerful Korosensei in order to prove that he was the strongest. He is also a brutally honest and direct individual. While under the influence of the tentacles, Itona mimicked Korosensei's interests and hobbies, examples being an interest in big boobs and eating the same snacks.

After being abandoned by Shiro and befriending Terasaka and his gang, Itona has since become more mellow and humble, and is now able to admit people are stronger than him, while still retaining his brutal honesty. He has also shown to be a very observant and creative individual. Thanks to Terasaka's words of encouragement, as well as Class 3-E's admiration of his abilities, Itona's desire to kill Korosensei became less self-centered and is willing to work together with Class 3-E, becoming much more sociable and involved with his classmates. His perversion, however still lingered as shown when he volunteered to use his self-built tank to look up the girls' skirts.

History
Itona is the son of Horibe Electronics Factory's former president. After his father's company went bankrupt, Itona was abandoned and sent to live with his uncle, which caused bullies to target him. They called him a weakling, with no money or home. This caused Itona's obsession with power and victory.

One night, Itona 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, and to become the strongest man in the world.

Transfer Student Time, 2nd Period
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 Shiota notes that two have probably had more than their fair share of problems, Karma Akabane 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 about 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 to 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.

Vision Time
Itona and Shiro make their second appearance following Takaoka's short stint as a PE teacher. The pair manipulates the isolated Terasaka in completing the preparations for their next strike. After Terasaka finishes spiking the newly-created pool with chemicals, Itona gets into his face stating that he has no vision and therefore weak.

The next day, Itona and Shiro activate their plan by having Terasaka unwittingly destroy the dam containing the pool water, making everyone in the pool swim uncontrollably towards the cliff. Itona strikes after Korosensei saves most of the students from danger, having planned this from the start. Korosensei, already weakened from the laced water and Terasaka's pesticide smoke bomb from the day before barely blocks Itona's tentacle but also keeping an eye on Sumire Hara precariously hanging on a cliff branch. When Terasaka realizes that he had been manipulated, he challenges Itona to fight him. At Shiro's order, Itona strikes Terasaka squarely in the chest with his tentacle. However, Terasaka catches hold of it and reveals that the shirt he wrapped around which still reeked with yesterday's pesticide spray. Since Itona had the same tentacles as Korosensei's, Itona sneezes and becomes disorientated. He is soon surrounded by the students (none too pleased at being used) who splash him with the same laced water while Korosensei saves Hara from danger. Recognising their strategy had failed, Shiro beckons Itona to retreat despite Korosensei once more requesting that Itona join the class.

Itona's Time
Itona makes a cameo return hearing about the class's unsuccessful attempt to assassinate Korosensei on Okinawa. Shiro concocts an elaborate plan to trap Korosensei by first using his perverted hobbies in framing him for committing heinous acts, then ambush him based on the class's strategies. Itona ambushes Korosensei when the latter is surrounded by anti-sensei fabric. By this time, however, Korosensei had anticipated the plan and easily countered Itona's attacks.

The repeated failures have now started to take a toll on Itona; the tentacles' power is consuming his consciousness. Not satisfied with this, Shiro abandons the boy and departs, leaving Itona to run away mentally unstable. He soon rampages throughout Kunigigaoka, attacking several electronic stores for a couple of nights. Itona is later cornered by the students but Shiro and his men kidnap the boy and threaten to kill him to lure out Korosensei. The class, however, are fed up at becoming collateral damage from Shiro's various plans, and grudgingly rescue Itona. Their success prompts Shiro to leave and rethink his approach.

Without the means to calm Itona's tentacles, Korosensei discovers that if not taken off, Itona will likely die. In the meantime, Itona's forehead was wrapped in an anti-sensei net made large bandanna to cover his tentacles. Terasaka and his group tried various methods to calm Itona down (one being Muramatsu's home-made ramen that Itona does not like) until the students discovered the key is Itona's background - the electronic stores. Once calmed down, Korosensei removes the tentacles. Itona is grateful for their assistance and finally joins Class E in their assassination. Due to Terasaka and his friends' involvement he begins hanging out with them, though still unimpressed by Muramatsu ramen.

Fitting in with Class E
Although his tentacles have been removed, Itona has retained some of his physical abilities. For instance, he was Class E's secret weapon during their athletic festival match against the numerically superior Class A and was instrumental in bringing Class A's pole down. His high level of intelligence has also been revealed when building and customising RC vehicles for reconnaissance purposes. Finally, he learns to be patient and wait for the right opportunity to strike - during the God of Death incident he realizes the huge difference in combat skills between him, Terasaka and the God of Death, and opted to surrender and wait for rescue rather than unnecessarily harming themselves.

In general, Itona has fitted in well with his classmates and his IQ was enough for him to be among the top 50 in the second semester finals. When Kaede Kayano launched a surprise attack on Korosensei prior to the end of the semester, Itona especially was surprised to see that Kayano also had tentacles. When asked for an explanation based on his experiences, Itona noted that Kayano must have endured a lot of pain to have been able to stay sane for so long. He and the rest of the class later witness her near-suicidal attempt on Korosensei's life, which ended when Nagisa kissed her and afterward listened to Korosensei telling about his past.

Schism Time: Class 3-E Civil War
Korosensei's story had dampened the class's enthusiasm to kill him. This came to the point where the class became divided over whether to continue killing their teacher or attempt to find a way to save him. Itona was among those who sided with the kill faction.

For much of the ensuing war, Itona tried to customise an RC drone for reconnaissance but failed, otherwise largely protecting Rinka Hayami from being killed. Eventually most of the few surviving 'save' team launched a frontal attack on the pair. Hayami took out two of them before being shot by Tōka Yada. Itona eliminates Yada from behind but is immediately cut down by Maehara, the last survivor of the attack.

Aftermath
After graduating from high school, Itona was revealed to be working at his father's factory. When he was asked what would happen if the factory collapsed like it had done previously, Itona simply replied that he would ask Muramatsu and Yoshida (who had both completed business management courses in preparation for taking over their respective family businesses) for help.

Abilities
Electrical Engineering: Itona has knack for gadgets and tinkering with electronic components due to learning the basics of technical and electrical engineering from his father's company and demonstrates excellent engineering skills, mostly notably in electrical engineering. He often puts his skills to good use with not just assassinations, but also in spying and reconnaissance when needed, being often tasked with using custom-made RC vehicles that he constructs for reconnaissance. He is also proficient in knowledge of electronic devices as demonstrated when he was able to safely remove the explosive collars from himself and from his classmates after they were kidnapped by The Reaper.

Intelligence: Itona was revealed to have a high level of intelligence that was hindered and couldn't be used due to his tentacles. He shows this through his mechanic skills and academic grades.

Athletics: While he had tentacles attached to his head, Itona had incredible physical abilities such as increased strength and speed that matches with Korosensei. After his tentacles were removed, he lost most of its abilities that could be on par with Korosensei, but he still retained most of his athletic abilities from his modification with Shiro, which 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 and brought Class A's pole to the ground.

Shiro
Shiro found Itona one night some time after his father abandoned him. Shiro fostered Itona by promising him the means for victory and power; with his technology, Shiro modified and equipped Itona with tentacles. However, Itona was merely a tool for Shiro's own goals, and was eventually abandoned after the tentacles eroded his mind.

Ryoma 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, Itona 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) "I might fail a hundred times, but I'll be sure to kill him before it's all said and done. You've got my back, right guys?"
 * (To his tentacles on what he wanted to be) "I want to be strong."
 * (Episode 14, to Ryōma Terasaka) "You. You're weaker than that red-headed fellow, even though you've got more raw energy and a better physique. Know how I can tell? There's no vision in your eyes. No will or way or want to win. The slow-witted cow who dimly chews the grass before it is no match for the wolf with a cow-killing vision."

Etymology

 * The name Itona means "yarn" (糸) (ito) and "become" (成) (na).
 * Itona's surname Horibe means "moat" (堀) (hori) and "department" (部) (be).

Trivia

 * Itona is one of the few students of 3-E to be called by his first name, the others are Nagisa Shiota and Karma Akabane.
 * Itona was called "Picture Book Graduate" during Class 3-E training using code names.
 * His favorite subject is Science, while his least favorite is Social Science.
 * His hobby/special skill is working with electronics.
 * His prized possession is "Itona 1", a prototype robot he built with Class 3-E.
 * His favorite food is Paitan Ramen.
 * Itona is the first student to discover Korosensei's heart was his weakness, most likely told by Shiro.
 * While under the influence of the tentacles, Itona 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.
 * Among the students in Class 3-E, Itona is the only one who sits in a row of students of the opposite gender (the rows alternate between all male students and all female students), sitting behind Kirara. If the seating arrangement was followed, he would've been sat behind Sosuke.
 * During the Civil War, Itona was eliminated by Maehara after the latter ambushed and knifed him during the attempt to also eliminate Hayami.
 * In the tankobon extras, Itona's statistics were listed as:
 * Physical strength: 2.5
 * Mobility: 4.5
 * Close-range assassination: 4
 * Long-range assassination: 2
 * Academic ability: 5
 * Characteristic skill: 4.5 (King of Inventors)
 * His statistics with tentacles at full power:
 * Physical strength: 5
 * Mobility: 5
 * Close-range assassination: 5
 * Long-range assassination: 5
 * Academic ability: 2.5