Yuma Isogai

"“Alright everyone! Let’s go in for the kill like always!!”" Yūma Isogai is a student in Korosensei's Class 3-E at Kunugigaoka Junior High School. He is the male class representative.

Appearance
Isogai has somewhat spiked dark brown hair with two small hair antennae at the top and brown eyes (pale gold in the anime). In addition to his personality, Yūma has been described as being very attractive and is one of the most popular members of Class 3-E. He's also popular with others from the main building and still receives love letters from females there despite the otherwise general discrimination.

In Koro Sensei Quest!, he wear a blue and white-coloured hero armor instead of school uniforms of his classmate, making him the most likely one to be a hero. However, it only cover Isogai's front via a rope tie and reveal his undressed back and white underpant, making him the most unlikely one to be a hero.

Personality
Isogai is a kind, cheerful, and reliable person. He is modest, not at all boastful, and helpful. Isogai has been noted to have good leadership qualities and personal virtues, and due to that he's able to see all the individual strong points in his classmates. Because of these traits, he is considered to be an ikemen, which not only means handsome, but can also imply a flawless personality.

History
Isogai comes from a poor family. He has an unnamed younger brother and unnamed younger sister who happen to have the same hair antennae as him and lives with his sick mother. His father died sometime during his first year in middle school, leaving him to take care of his mother and their finances. To keep their expenses from going up, especially from their combined tuition struggles, Isogai began working part-time despite knowing that school regulations stated students weren't allowed to have jobs. He was dropped at class E because he violating school policy.

Plot
Out of all the students in Class E who aren't primary perspective characters or primary characters in general, Yūma is among the most seen. While his official introduction wasn't until Chapter 90, his first notable appearance was during the Finals Arc where he was the rival to Teppei Araki in Social Studies.

Leader Time - Athletic Festival Arc
The Athletic Festival Arc is where Isogai makes his formal debut. It starts out in Chapter 90 where a few of his classmates are visiting him at his part-time job. While Isogai is attending to two regular customers, they note that he truly is an ikemen (with one of them, most likely Okajima, noting they want to kill him for it). They then began to basically state how incredible their leader is at everything and Korosensei, who was revealed to have come there for some honey toast, ask them if they're bothered by Isogai no matter how much of an ikemen he is. They say no and he asks why is that and Maehara just simply says that Isogai is just a nice guy, earning the agreement of his peers. Then, a few more customers come in who are none other than the Five Virtuosos who found out about Isogai's part-time job. One of the regulars come to Yūma's defense and Ren Sakakibara charms her and tells her it's a school matter so they'll take it outside. Outside Isogai begs Asano to keep it a secret since he needs the part-time and Asano states that he would also like to as well, but on one condition: Isogai and the rest of Class E show him their fighting spirit at the athletic festival's Bo-taoshi match.

The next day Class 3-E is discussing this and note the unfairness of the entire setup. Isogai, not wanting anything to happen to his companions, states that he'll shoulder all the responsibility. This elicits angry remarks and some students (particularly Karma and Nagisa) throw stuff at him. The class calls him an idiot for thinking he'd be alone in this and Maehara tells him to not think too much. He slams an Anti-Sensei Knife on Yūma's desk and says it'll be easy beating the nerds in Class A at bo-taoshi. Other students then jump in and agree, saying that this match will be a good chance to get back at them for all they've done to them. Isogai is touched by this and declares that they're doing it.

It's the day of the athletic festival and while his classmates are going through their events, Isogai is working on the strategy for the bo-taoshi. As Class E show their hidden strengths, Korosensei says that if only that unpredictability was used by assassins and that the foundation of strength, balancing abilities, kinetic vision, and sense or which have been strengthened through assassinations will show in non-everyday competitions. He also says that in such ways those individual personalities become a weapon and how that will be capitalized in the bo-taoshi will depend on Isogai. While the students of Class E decide to focus on the final bo-taoshi, they find out what Asano had been planning and his true goal which were in the form of four huge foreign 14-15 year old top sportsmen. As Asano is talking to two of them, Isogai starts to feel insecure as his abilities aren't anywhere near Asano's. He starts to feel conflicted and begins worry about his team. Korosensei tells him that in society there's a limit to one person's abilities and in terms of the ability to lead and fight with friends, he surpasses even Asano and even when he falls into a pinch, everyone will fall with him and fight and that is his personal virtue. Korosensei then said that he's glad that he was able to be Isogai's homeroom teacher. After that it's time for the bo-taoshi to start and both teams line up. Class A is given the advantage once again by being allowed to wear headgear and long sleeves, but Class E doesn't let that deter them as they enter their initial formation: the Ultimate Defense Form.

Both classes battle it out fiercely during the match. During one particularly tight spot, Isogai thinks back to a previous lesson about Hannibal of Carthage and how he led his small army to victory through wit and thinking outside the box. With that in mind, he leads his team and the Class A students who are chasing them to the stands since there was no rule saying they had to stay inside the field. Class E continues evading Class A until finally Muramatsu and Yoshida appear, revealing that being knocked out earlier had been a ploy. Isogai then tells everyone they're done running and calls for the next formation, "Speed of Sound." Those of Class E who were on offense rush toward Class A's pole. With all them in they proceed to corner Class A and shake the pole down. As a last resort, Asano starts attacking and at some point strikes down Isogai who reveals to have used that to add four more students to the mix. Finally, Isogai calls for their secret weapon, Itona and launches him six feet in the air onto the pole and bringing it down giving Class E the win.

After the match, as everyone is cleaning up, a few underclassman congratulate Isogai. Eventually, Asano shows up and Maehara asks him if he's going to keep his end of the bargain to which he states that he doesn't lie nor use underhanded methods like they did. Isogai comes up and congratulates Asano on his command and tells him they should have another match some other time. Asano simply walks off and gives a snide remark but Isogai isn't bothered by it in the least. While everyone calls him a sore loser, Takebayashi states that Asano has been going through a lot like Isogai the latter of who says that his situation doesn't even compare. Even so, having everyone get together to help him made him grateful that he was poor. After that Nagisa notes that Isogai isn't flashy like Asano is nor is he out front or top, he's right there next them, an assassin and ikemen. The arc then closes with Isogai begging to take home the leftover bread from the bread race.

Time to Choose
"“Who does not want to kill Korosensei?”"

"(everyone raises hands)"

"“Who wants to kill Korosensei in his favor?”"

"(everyone raises hands)"

Eventually emerging out as a victor in the battle with Shiro and after miraculously reviving Kaede from the dead, Korosensei collapses due to exhaustion and injuries. With less than half an hour away until Lance of the Heavens (the military space satellite specially constructed to kill Korosensei) fires its antimatter beam, Korosensei addresses Class 3-E that the assassins should not miss their dying target and that the inevitable has come. He further states that all good times must come to an end, hence the classroom. Isogai asks the Class 3-E whether they should assassinate Korosensei by themselves, or to leave him to his fate at the barrel of a satellite battery. All in class 3-E, including himself, chooses to assassinate their teacher in his favor so they can maintain their bonds forged with their beloved Korosensei as assassins and a target. With everyone holding tentacles, Nagisa volunteered as an executor and no one in Class E are complaining about it.

After the graduation, Isogai was shown "unable to compute" the large reward money they received from the government. Eventually the class decided to donate some of the money to various organisations (the nursery being a prime example), used a portion to cover their education and living expenses and purchased the mountain classroom. The majority of the money was then handed back to the government, with Isogai representing the class. Seven years later, Isogai led some of his former classmates to clean up and renovate their former classroom, finding Kayano there. Isogai also wondered how they will be able to look after the place once life in general will occupy their time.

Abilities
Knifework: Isogai excels in knifework and is considered the best out of all the boys in Class 3-E (and the class as a whole).

Marksmanship: Isogai is ranked second for marksmanship of the boys' side (and the class as a whole), scoring 103/200 in June.

Social Studies/Geography: Yūma is ranked 1st in the school for Social Studies.

Other Skills: Yūma is known to have excellent reflexes and is good at sports.

Leadership: As a male class representative and leader of Class 3-E, Isogai has excellent leadership.

Hiroto Maehara
Isogai and Maehara are really close friends and are often seen together. With their excellent reflexes, the two can become formidable opponents when teamed up. They lived in the same neighborhood when they were little and have been best friends since elementary school, and as a result they understand each other the most. Maehara is important enough to Isogai to have been listed as his treasure, alongside his family. Isogai also happens to know Maehara's entire dating history.

Megu Kataoka
Isogai and Kataoka are fellow class representatives. They often work together and are considered the leaders of Class E. The two are also shown to have a good friendship. Their relationship is mostly work based, but Class E rumours about what is the real nature of it.

Quotes

 * "Harmonise everything, shrink your finances." Election Headline (from the 1st Popularity Poll)
 * (Talking about the Red Faction, Chapter 144) "Probably those who have a certain confidence in their skills are able to make harsh decisions."

Trivia

 * His favorite subject is Geography/Social Studies while his least favorite is Biology.
 * He's considered to be the most attractive guy in Class E by the girls.
 * Though right-handed, he is seen batting left-handed, making him ambidextrous as well.
 * His hobby/special skill is tennis, it was also his previous club before dropping to 3-E.
 * In the tankobon extras, it was stated that his classmates want to yank the two antennae sticking out at the top of his head out of jealousy for his talents.
 * The extras reveal that, when he's feeling sick, his hair antennae wilt. Upon noticing this, all of his classmates made him take a break. In the character book, Mimura says he's able to guess Isogai's current condition by seeing his antennae.
 * He was called "Poor Committee Member" during Class 3-E's training using codenames. The one who wrote his codename was Maehara.
 * In the popularity poll of Volume 12, he was the highest ranked student outside the main trio, at 6th place.
 * He has the highest overall statistics out of all of the students.
 * During the Civil War, he was eliminated during the sacrificial attempt to eliminate Hayami.
 * His motto is "If the cuckoo bird won't sing, let's all sing".
 * His father is stated deceased after a traffic accident by Yusei Matsui.
 * In the tankobon extras, his statistics were listed as:
 * Physical strength: 4.5
 * Mobility: 4
 * Close-range assassination: 5
 * Long-range assassination: 4.5
 * Academic ability: 4.5
 * Characteristic skill: 4 (all-purpose adaptability)
 * In Koro Q, Isogai's bug is that he can only wear the front of his equipments, while being naked only with his underpant by back.