When he was three years old, he woke up in the middle of the night to use the restroom. When he rubbed his eye, his Quirk manifested for the first time. This made his hand harden and caused Eijiro to cut himself, which left a scar on his right eye.
Eijiro and Mina attended the same school during Junior High and although they were not close, Mina's outgoing nature and strong personality made Eijiro self conscious of his own appearance and personality. This was worsened during an incident where Eijiro found himself unable to stand up against a figure who was threatening fellow students of his school. This incident left Eijiro feeling wholly incapable of being a Hero primarily due to his hesitation in risking his life to save others. 
Afterwards, Eijiro accidentally came across an old holographic projector depicting an interview with Crimson Riot. The words of Eijiro's idol, which had inspired him before, again inspired him further to keep following his dream of attending U.A. High School. Eijiro committed to training himself in order to pass the the U.A. Entrance Exam.
The morning before classes started at U.A. Eijiro met up with Mina again. Sporting a new hairstyle, Eijiro claimed to have left his insecurities behind, but Mina playfully told Eijiro to not pressure himself too much and let the change just happen naturally once Eijiro became truly confident about himself.
Eijiro participates in the U.A. Entrance Exams and his efforts allow him to place second overall.
Eijiro Kirishima is first introduced when Izuku Midoriya arrives on the first day of class. He is sitting at his desk, alongside the other Class 1-A students. Shortly afterwards, the class makes their way to the P.E grounds, where Shota Aizawa informs them they must undertake a Quirk apprehension test. Eijiro is shocked by his teacher's announcement that the student who would place last would be expelled.
The next day at school, All Might teaches Class 1-A's Basic Hero Training Class and announces that the class will participate in Battle Trials. Eijiro is excited by the idea of combat training and changes into his hero costume with the rest of his class. Eijiro is partnered with Hanta Sero on "Team J" after being randomly paired.
While observing the battle between Katsuki Bakugo and Izuku Midoriya, Eijiro says Katsuki I s unmanly for trying to ambush Izuku. He also questions what they're saying during the battle, as there's no sound through the surveillance footage. After witnessing Katsuki's large attack on Izuku, Eijiro becomes increasingly concerned about Izuku's safety.
Watching the match between Shoto Todoroki vs Mashirao Ojiro and Toru Hagakure, Eijiro and All Might begin to shiver when Shoto uses his Quirk. Later on after the battle trials, when Izuku returns to class, Eijiro along with his other classmates surround him praising his performance during the Battle Trial and introduce themselves.
During their next homeroom class, Mister Aizawa announces Class 1-A must choose a class president. Eijiro and his classmates are excited by the idea of representing their class. After voting, Izuku Midoriya is elected and Eijiro openly supports him.
Later on, the school sirens go off at lunch and students evacuate in a panic, creating a large traffic jam. Eijiro is caught in the mob, but the situation is diffused by Tenya Iida, who reveals it is a false alarm caused by the media trespassing on school grounds. Afterward, Izuku resigns as class president and nominates Tenya in his place. Eijiro supports the decision because he saw that Tenya manned up and took charge of the previous situation.
Shota interrupts and instructs the class to suit up and prepare to head out for rescue training. While on the bus traveling to an outside facility, Eijiro speaks with his classmates regarding Quirk's and their relation to pro-heroes popularity. He says that he wishes for a flashier Quirk, believing it would garner him more fame. Izuku argues that Eijiro's Quirk is strong enough to become a popular pro, but Eijiro restates his point by using Shoto and Katsuki as examples of Quirk's perfect for professional heroes.
The class eventually arrives at the Unforeseen Simulation Joint, greeted by Thirteen. But they are interrupted by the arrival of the League of Villains. As the villains keep showing one after another, Eijiro is seen evacuating with his class, but they end up coming across Kurogiri, who blocks their way. Eijiro, together with Katsuki, attempt to attack the villain but are unsuccessful due to Kurogiri's amorphous body. The villain then uses his Quirk and warps Eijiro, along with Katsuki, to the Ruins Zone of the U.S.J.
In the Ruins Zone, Eijiro and Katsuki are ambushed by a group of villains, but both are able to hold their own and easily defeat them. Eijiro says that they should go and save the others, worrying about his classmates that do not have battle-effective Quirks. Katsuki, however, decides to go and fight Kurogiri instead, much to Eijiro's surprise. After hearing Katsuki's reasoning to go after Kurogiri, Eijiro notices Katsuki's calm attitude, much to Katsuki's chagrin. Eijiro decides to go with Katsuki.
Eijiro and Katsuki eventually reach the central plaza, where they attack Tomura and Kurogiri respectively. Eijiro attempts to punch Tomura, but the latter evades him. Eijiro expresses his desire to support All Might, but the hero refuses and tells them to escape instead. Tomura attempts to attack Eijiro and the others, but All Might's fight with Nomu prevents him from getting close. Eijiro and the others watch in awe of All Might's strength as the Number One Hero defeats the Nomu.
Eijiro withdraws himself from the rest of the fight, but witnesses Izuku rushing to All Might's side. Izuku and All Might are both saved when Tenya returns to the U.S.J. with pro heroes as reinforcements. After the remaining villains are defeated, Eijiro rushes to check on Izuku's condition. Cementoss arrives and blocks Eijiro's way, before he discovers All Might's weak form. He instructs Eijiro to regroup with his class. Eijiro follows the heroes instructions and joins his class outside the facility before returning to school.
Two days after the attack on the U.S.J., Eijiro and his classmates return to school and talk about the attack. After Mister Aizawa returns to class, Eijiro and his peers are lectured about the importance of the upcoming U.A. Sports Festival. Eijiro is more than excited to participate despite some of his classmates concerns over holding the Festival soon after the attack. Eijiro is freaked out when Ochaco Uraraka gets overly excited and demands the class chant that they will do their best.
At the end of the day, Class 1-A's exit gets blocked by a crowd of students from other classes. Katsuki confronts and insults the crowd, making enemies out of everyone else before leaving. Eijiro tries to get Katsuki to defend the class, but he replies that the crowd of students are irrelevant and it's only important that he defeats them. Eijiro is moved by Katsuki's "manly exit".
For the next two weeks before the festival, Eijiro trains at the Replica City District. When the day of the U.A. Sports Festival arrives, Eijiro changes into his P.E. clothes and prepares with his class in their designated waiting room. Like the rest of his peers, Eijiro takes notice when Shoto Todoroki challenges Izuku Midoriya. He tries to diffuse the situation, but Shoto refuses him and replies that the festival isn't a team effort.
Before the festival begins, First Year Chief Referee: Midnight calls Katsuki to the stage to lead the pledge. Instead, he simply announces that he will win the games, angering his fellow competitors and generates booes from the crowd. Eijiro and his classmates aren't surprised, they expected Katsuki to say something like that. Midnight announces the preliminaries will be an Obstacle Race four kilometers around the stadium, which immediately begins after the rules are explained. Shoto gets out to an early lead by freezing the stadium's exit, but Eijiro avoids the ice by jumping through the exit. Next, everyone reaches the first obstacle: a blockade of Villain-bots from the entrance exam, including several giant Zero-Point Villains.
Shoto freezes one of the giant robots solid while it's off balance, causing it to fall on Eijiro and TetsuTetsu from Class 1-B. Eijiro survives by using his hardening Quirk and damns Shoto for endangering others like that. Eijiro believes only he could have survived, but is shocked when TetsuTetsu uses his Steel Quirk to break free from underneath the robot as well. Eijiro is discouraged when he notices TetsuTetsu's Quirk is similar to his own, fearing he won't be able to stand now. Eijiro finishes the Obstacle Race in ninth place, qualifying him for the second event: The Cavalry Battle.
After Midnight explains the rules, everyone forms their teams for the Cavalry Battle. After failing to team up with Shoto, Eijiro asks Katsuki to form a team. Katsuki forgets Eijiro's name and greets him by "dumb hair". Eijiro takes exception to this and says their hair styles are similar. Eijiro understands that Katsuki will need a strong front horse for the Cavalry Battle and his Quirk would be perfect for resisting Katsuki's explosions. Katsuki replies that he needs someone with guts, and Eijiro convinces him to form a team by promising to go after Izuku Midoriya's team together.
The Cavalry Battle begins and like many of the other teams, Team Bakugo goes after Team Midoriya's ten million points. Katsuki tries to attack them in the air, but is blocked by Fumikage Tokoyami's Dark Shadow Quirk. Fellow member of Team Bakugo, Hanta Sero catches Bakugo, garnering Eijiro's praise. Soon after, Team Bakugo's points are stolen by Team Monoma. Neito Monoma from Class 1-B taunts Katsuki, enraging him. An angry Katsuki tells Eijiro that their plans have changed: before they go after Team Midoriya, they must destroy Class 1-B.
Neito evades Katsuki's first attack and then blasts him with an explosion. Surprised, Eijiro comments that it's weird Neito is using Katsuki's Quirk. Then Neito quickly taps Eijiro's forehead before blocking Katsuki's next attack. When the smoke clears, Eijiro is shocked to see Neito is using his hardening power to defend himself. Katsuki figures out Neito's Quirk is the ability to copy other powers.
Katsuki tries to attack again, but Eijiro is immobilized by Kojiro Bonto's Quirk and Neito flees. The next time Team Bakugo is able to get close, Katsuki flies off and attacks on his own. Although Eijiro warns him not to fly off on his own, Katsuki is able to steal enough points to move his team to second place. Eijiro is satisfied, but his team leader is anything but. Katsuki demands that they take the rest of Team Monoma's points before going after Izuku's team. Using Hanta and Mina's Quirks strategically, Team Bakugo charges at Neito and Katsuki takes back their original headband. They go after the ten million points, but time runs out just as they arrive on the scene. Hanta is happy with second place, but Eijiro notes that Katsuki is not satisfied at all, as they all watch him scream in anger.
Midnight announces the finals will be a One on One Fighting Tournament and everyone draws lots to see who they will face in the first bracket. Eijiro expresses his excitement to participate in the finals he has watched every year growing up. He matches up with Tetsutetsu, much to his irritation.
Eijiro duels Tetsutetsu in the seventh match of the first round. They receive similar intros from Present Mic, further annoying Eijiro. He and Tetsutetsu fist fight using their hardened bodies, trading blows back and forth until they eventually knock each other out. Midnight rules that after they both recover a victor will be decided via an arm wrestling contest.
Once the last match of the first round ends the arm wrestling match commences. They both use their Quirks to try and gain an advantage, but Tetsutetsu's iron gives way and Eijiro pins his arm down to win and move on to the next round. Eijiro offers his hand to Tetsutetsu, congratulating him on a match well fought. Tetsutetsu shakes Eijiro's hand and thanks him for the compliment.
Eijiro returns to his class just after the start of Izuku and Shoto's battle. He's upset at himself for arriving late but Denki congratulates him on his victory. Eijiro thanks him and comments that Katsuki is next, to which he replies that he'll kill Eijiro. Eijiro laughs him off and responds by sarcastically complimenting Katsuki for having moves that blast the whole stadium. Katsuki tells Eijiro and Denki that Quirk's are physical abilities and they all have their limits.
In the last match of the second bracket, Eijiro faces off with Katsuki. Eijiro cuts Katsuki's cheek near the start of the bout and takes an explosion straight to his hip. Eijiro is unphased thanks to his Quirk's defensive ability.
He taunts Katsuki, telling "explosion boy" that his blasts will not work and goes on the offensive by trying to deliver a series of punches. Katsuki evades the strikes and is eventually able to injure Eijiro with another direct hit to his torso. Katsuki figures out that Eijiro's hardening ability weakens with every hit, and that he has been overusing it to keep his entire body hard throughout the fight.
Katsuki capitalizes and unleashes a flurry of explosions until Eijiro is ultimately overwhelmed and knocked unconscious. Eijiro is treated for his injuries and returns to the stands in time for Katsuki's next round fight against Fumikage Tokoyami. Fumikage ultimately surrenders and Eijiro surmises that his Quirk is weak against light, and Katsuki was the perfect person to exploit that.
Along with his class, Eijiro watches the closing ceremony of U.A.'s Sports Festival. He comments that Katsuki has been in a fury ever since he woke up after being knocked out at the end the finals.
Eijiro returns to class two days after the Sports Festival. Mr. Aizawa teaches them about Hero Informatics and Eijiro fears the topic may be on hero laws. He's excited to learn that the class will choose their hero names for upcoming internships. Aizawa reveals the draft results prior to the festival and Eijiro received sixty-eight offers from Pro-Heroes.
Midnight joins the class to help them select hero names for their upcoming internships. Eijiro chooses the moniker Sturdy Hero: Red Riot. Midnight questions whether this name is a nod to an old school hero Crimson Riot, which Eijiro confirms. Eijiro replies that although he's old school, Crimson Riot is his idol and he wishes to be just like him. Midnight advises him to live up to the name and Eijiro tells her that he will.
After Class 1-A is finished formulating their hero names, Eijiro is given his list of offers so he can choose a Hero Agency to intern at. He wishes to fight crime in a big city and elects to choose Fourth Kind's Agency. When first day of the internships arrive, Katsuki receives his costume and boards a train to Fourth Kind's agency.
Eijiro meets Tetsutetsu at the Fourth Kind's Office, surprised to see his newfound friend there. Fourth Kind explains that his office were able to extend two offers because he was impressed with the two young men's spirit. The Chivalrous Hero teaches them about hero wages from the government.
The next day, Eijiro and Tetsutetsu make lukewarm tea as they are punished by Fourth Kind. He punches both of them with their Quirks active and says it is satisfying to hit their hardened bodies, hiding that he is in pain.
The workplace training comes to an end and Eijiro returns to U.A. In Class 1-A, Eijiro and Hanta laugh at Katsuki's new hairstyle, causing Katsuki to retaliate in anger. Later on, he and the class witness the field training race with Eijiro voicing Hanta will win after Hanta leads in it. However, Eijiro is surprised when Izuku suddenly passes Hanta up, he is amazed at the latter's new moves.
After Foundational Hero Studies is finished, Eijiro is in the boys' locker room changing into his school uniform. He states that he needs to focus on his maneuverability.
One week before final exams, Shota reminds Class 1-A to study for their written and practical components before ending class. Many of the students opt to study with Momo, and Eijiro mentions how he should tag along. Irritated, Katsuki says that he'll beat the material into Eijiro's head himself and Eijiro responds that he'll be counting on it. When Katsuki scolds everyone for their excitement and storms out of class later on, Eijiro mentions it's been a while since Katsuki has been that intense. Eijiro later studies with Katsuki as they prepare for the tests. A week passes and Class 1-A finishes the written section of the finals. They change into their hero costumes and join their teachers at the practical exam area. There, Principal Nezu announces the practical portion will involve pairs of students facing off against one teacher. Eijiro and Rikido are paired against Cementoss in the first bout.
Eijiro and Rikido agree to attack Cementoss from the front because he's slow, but their opponent creates multiple cement walls to block them. Eijiro and Rikido use their Quirks to smash through the cement blocks, but Cementoss continues to make more. Before long, the tandems Quirks run out of steam and Cementoss defeats them using a cement attack, and as a result, they fail the practical.
Eijiro and Rikido mull over their defeat as the remaining matches are underway. Following the conclusion of final exams, Class 1-A returns to their homeroom. Eijiro, Rikido, Denki and Mina are all crestfallen that they are unable to go to training camp because they failed the practical. Izuku tries to cheer up those who failed, but Denki launches a comical tirade at Izuku. Soon after, Aizawa enters the classroom and informs Class 1-A that all of them are going to the training camp. Eijiro and the others are happily shocked to hear this, but they will all receive harsh extra studies for failing. Class 1-A decides to go to the Kiyashi Ward Shopping Mall to buy necessities for the forest lodge. Eijiro asks Katsuki to tag along, but he refuses. At the shopping mall, Eijiro sees that everyone has different needs and suggests splitting up and meeting up later.
A day prior to summer break, Izuku invites the boys from Class 1-A to the pool for endurance training. Eijiro arrives late with Katsuki in tow. They hold competitive swimming races and Eijiro loses his leg to Katsuki. Just before Shoto, Izuku, and Katsuki compete in the final race, Shota arrives and tells them they're out of time to use the pool and kicks them out.
Summer break begins and Class 1-A rides a bus to a forest reserve belonging to the hero team: The Wild, Wild Pussycats. Pixie-Bob and Mandalay introduce themselves and challenge the students to reach base camp past the forest in three hours. When most of Eijiro's peers refuse, he and his class are forcibly thrown into Beast's Forest by Pixie-Bob's Quirk.
Monsters made from dirt clods attack the students. Class 1-A works together to fight their way through Beast's Forest. They encounter several different dirt monsters. Eijiro and Rikido use their enhanced strength to destroy one of the monsters after Hanta slams it into the ground with his tape.
Class 1-A doesn't make it through the forest for several more hours. Well over their time limit, Class 1-A arrives at the base camp exhausted and battered. Mandalay reveals the time limit was the expectancy for actual heroes, not the students. The Pussycats serve the students dinner. Eijiro and Denki scarf down their food while complimenting how good it is. Eijiro gets a whiff of meat in a clay pot and erratically asks Pixie-Bob about it while his mouth is full. She replies that the boys are so hungry that they're acting strangely. Eijiro and the boys bathe in the hot springs afterward.
Intense Quirk Training begins the next day. Eijiro trains his Quirk by fighting one on one with Mashirao's tail. Afterward, Class 1-A and 1-B are tasked with cooking for themselves. They successfully make curry for everyone. Eijiro says it doesn't taste great but he's so hungry that it doesn't even matter. Eijiro and the other students who failed their practicals take extra lessons with Shota until two in the morning. Training starts back up at seven the next day. Eijiro, Mina, Denki, Rikido, and Hanta are all super tired, but Shota forces them to train anyway.
The Pussycats offer the students a test of courage activity following training. Shota, however, forces the extra lessons group to sit out for more teaching, much to their displeasure. The Vanguard Action Squad of the League of Villains invade that night. Mandalay sends out a telepathic message warning the students of their arrival. Shortly after Shota leaves, Mandalay sends out two more messages giving permission for students to fight back and informing everyone that Katsuki is one of the villain's targets.
Frustrated with his inability to save Katsuki, Eijiro pleads with Vlad King to let him fight. The hero refuses until they're interrupted by a sudden attack from Dabi. Dabi blasts the classroom door open with a fire attack before being quickly subdued by Vlad King. Dabi taunts Vlad King and the students, saying that they've already failed. Shota returns to the class and destroys what turns out to just be a clone of the villain. Eijiro and Tenya plead for Shota to allow them to fight, but he refuses as well.
The villains successfully kidnap Katsuki and the students return home from camp. Two days later, Eijiro visits Izuku in the hospital along with many of his peers. Eijiro tells Izuku they can still save Katsuki. The day before, Eijiro and Shoto overheard Momo tells All Might about a tracking device she placed on Nomu.
Tenya deduces that Eijiro wants Momo to create another receiver so that Eijiro and company can track down and rescue Katsuki themselves. He demands that the rescue of Katsuki be left to the pro heroes, but Eijiro is tired of being unable to do anything. This leads to a heated argument between the two. After being calmed down by Denki and Tsuyu, Eijiro admits he's fully aware that the matter should be dealt by professionals. Even so, Eijiro encourages Izuku to go through with the plan because they can still save their friend.
Most of Class 1-A are against the plan. After the doctor requests the class to leave, Eijiro tells Izuku that he and Shoto will be waiting outside the hospital tonight for him and Momo so that they can go and rescue Katsuki.
Later that night, Eijiro and Shoto wait for Izuku and Momo. They arrive, but before Momo can speak, Tenya appears, angry that they are about to repeat the same mistake he made at Hosu. Shoto tells Tenya that they will not engage the villains in combat, and Eijiro explains that they are planning a covert mission. Momo states that she came along to accompany them all in order to prevent them from engaging in combat. Tenya decides to go with them.
Eijiro along with Izuku, Momo, Tenya and Shoto board a train to travel to a place called Kamino Ward, located in Yokohama City in the Kanagawa Prefecture. At the location, the group puts on disguises to prevent the League of Villains from recognizing them. They exit the clothing shop and witness a video clip of U.A.'s public apology for the danger.
Eijiro along with Shoto, Izuku, Momo and Tenya continue towards the place that Momo's tracking device is detecting. After waiting for a while near the place, Momo, Tenya, Shoto, Eijiro, and Izuku prepare to infiltrate the supposed League of Villains' hideout.
Eijiro along with the group go to the back of the hideout and see a window. Shoto and Tenya have Izuku and Eijiro stand on their shoulders to see what is inside using the night-vision goggles Eijiro brought along. Suddenly, Mount Lady destroys the front of the warehouse which shocks Eijiro.
Seeing that the Pro Heroes are at the warehouse, Eijiro and the group assume that All Might is with Katsuki as they are speaking. Eijiro and the group decide to head home. Suddenly, the entire warehouse is completely destroyed by a mysterious man along with the surrounding area being significantly damaged. The man's aura above them utterly terrifies Eijiro, Izuku, Shoto, Tenya and Momo, with them all unable to move from their spot.
As the conflict continues, Eijiro watches the man battle All Might and sees there are no openings to rescue Katsuki, due to All For One's presence and Katsuki being outnumbered by the Vanguard Action Squad. Suddenly, Izuku comes up with an idea and explains the plan to Eijiro and the rest of the group. He tells Eijiro that the plan will depend on him since he is the only one whose help Katsuki won't be ashamed to accept help from.
Izuku puts his plan into action; Izuku and Tenya hold onto Eijiro with Izuku using One For All Full Cowl and Tenya using his Recipro Burst to burst through the wall while Eijiro uses his Hardening to protect himself, Izuku and Tenya. After Izuku, Tenya and Eijiro burst through the wall, Shoto creates an ice ramp; Izuku Tenya and Eijiro jump off Shoto's ice ramp and head into the sky. All For One sees the trio and attempts to attack them, but All Might intervenes by punching him. Katsuki sees the trio while Eijiro yells at Katsuki to take his hand. Tomura tries to take Katsuki, but Katsuki uses his Explosion to launch himself towards Izuku, Tenya and Eijiro. Katsuki grabs Eijiro's hand and smiles.
Seeing that Izuku, Eijiro and Tenya have succeeded in rescuing Katsuki, Shoto and Momo begin escaping from the battlefield. Shoto and Momo successfully escape. Shoto phones Izuku and finds out that him and his group are at the train station. Shoto and Momo meet up with Izuku, Eijiro, Tenya, and Katsuki. They take Katsuki to a Police Station for his safety. Afterwards, Eijiro parts ways and goes home. He then goes home after bringing Katsuki to the police.
Following the intense villain attacks toward U.A. students, Nezu transformed U.A. into a boarding school in order to protect the students. The Height Alliance was built in just three days. It is meant to protect the students and allows the teachers to keep close surveillance on the students.
Shota Aizawa meets with his students outside of the building. He states they must start preparing to get provisional hero licenses like they had planned to during the training camp. Then Shota expresses his disappointment that some of them tried to act like they had their licenses; Shota calls out Eijiro, Izuku, Shoto, Momo and Tenya. Shota tells them that he knows that they were present at the site of Katsuki Bakugo's rescue and took it upon themselves to rescue him. He also knows that the rest of Class 1-A, except Katsuki, Toru Hagakure, and Kyoka Jiro, also knew about their plan to rescue Katsuki. Shota explains that their actions have been covered up but tells them that if All Might did not retire, with the exception of Katsuki, Toru, and Kyoka, he would have expelled them all as punishment. Shota advises the group that went to save Katsuki to go through the proper procedures next time which will also restore the trust between them.
The atmosphere of Class 1-A has become gloomy. Katsuki sees the gloomy atmosphere and grabs Denki and forces him to use his Electrification to get him into his dumb state to distract the class. He then pays Eijiro back for using his allowance on night vision goggles. Eijiro promises to make it up to the class by buying them dinner later that night.
Class 1-A arrange their luggage in their respective bedrooms. Later that night, the boys of Class 1-A are in the common space on the first floor. The girls of Class 1-A show up and Mina Ashido suggests a room showcasing competition. When they check out Eijiro's room they see that it is full of manly elements. None of the girls, except Ochaco, appreciates Kirishima's room. After the competition, at Ochaco's urgings, Eijiro along with Izuku, Shoto, Tenya, and Momo all meet outside the dorm where they find her with Tsuyu. Tsuyu apologizes for harshly doubting their plan to save Katsuki, and they apologize for worrying her and they mend their friendship.Eijiro and the rest of Class 1-A are charged with coming up with new special moves and are given a special class to develop their Quirks and come up with them. During the class All Might shows up and advises Eijiro to focus being less artful and more on utilizing brute force with the technique he should develop. Eijiro also updates his hero costume and adds sleeves to it to protect civilians he is rescuing from being hurt by his Quirk.
The day of the licensing exam arrives and Class 1-A travels to the National Dagobah Arena. The first phase begins and Izuku suggests that Class 1-A stick together, but Katsuki refuses and goes off on his own. Eijiro and Denki follow Katsuki to a streetside area of the arena. Katsuki yells at them both to stop talking and Eijiro replies telling Katsuki to relax. A mound of flesh is thrown at Katsuki and Eijiro throws himself in the way to save his friend. The flesh attack transforms Eijiro into a meatball that lands in Seiji Shishikura's hand.
Later, Katsuki would also be transformed into a meatball, but both are saved by Denki, who manages to injure Seiji and he loses his hold on the meatballs. Katsuki and Eijiro return to normal and both deliver the finishing blow. Katsuki, Denki, and Eijiro manage to eliminate two people each and pass the first exam.The second phase of the exam begins and Katsuki rushes off on his own again. Once again Eijiro and Denki follow him through the arena.  Katsuki refuses to help other people that Denki and Eijiro decide to rescue, being very rude to them. The exam ends after Denki and Eijiro save the last two people from H.U.C.  Everyone meets to look over a presentation board revealing who passed the exam. Kirishima sees that he has managed to pass the exam and get his license, but he is surprised to see that Katsuki does not. Katsuki is livid to find out that he failed the exam. 
Shota tells to Class 1-A the Hero Internships, hero activities done off campus, saying that it is a more formalized version of the Field Training they did with pro heroes before. Three days later, Shota Aizawa introduces Class 1-A to the people who will teach them about Hero Internships; the third-year students who rank among the top of all U.A. students known as The Big 3: Mirio Togata, Tamaki Amajiki and Nejire Hado.The personalities of the three students leave Class 1-A confused, who get even more confused when Mirio Togata challenges them all to a fight. At Gym Gamma, Eijiro Kirishima note that they have the advantage and Eijiro asks Mirio if he sees them as nothing but small fry, to which Mirio replies he does. Mirio tells Class 1-A to attack him whenever, wherever they want and asks who wants to go first. Izuku and Eijiro decide to go first. Surprised at Izuku's determination, Eijiro lets Izuku go first.
Izuku attacks and kicks at Mirio head, but his foot phases clean through Mirio's head and the former confirms Mirio's Quirk allows him to pass through things. Using his Permeation Quirk, Mirio easily defeats more than half of the entire class 1-A. The other half tries to counterattack, Deku having discerned the functioning of his Quirk, but still Mirio also defeats them with hardly any problem. As Class 1-A recovers, Mirio states that the reason he wanted to fight Class 1-A is to show the experience he gained from the Hero Internships; Mirio was able to transform his Quirk and reach the top. Class 1-A start seeing that Hero Internships are different from the Field Training they went through.Following Mirio's advice and with help from Tamaki, Kirishima end up interning under Fat Gum. Eijiro thanks Fat Gum for employing him after Fourth Kind refused to employ Eijiro. They are in the Kansai Region, patrolling the streets in the Esuha Market. Suddenly, a fight breaks out. A thug is attacking another group of thugs for doing business on his turf. The group of thugs manage to get away, only for them to land into Fat Gum, and start submerging into his body. However, one of them manages to escape, but is caught by Tamaki's Quirk. Tamaki wonders if he did a good job, to which Eijiro replies that he was awesome.
However, another hidden criminal watching from the crowd shoots Tamaki with a mysterious bullet. He fires off a second shot but Red Riot deflects it off his own head using his hardened skin. Fired up, Red Riot hardens his whole body and leaps into action.
Tamaki tries to use his Quirk again but for some reason he can not activate it, and Fat Gum is surprised to learn the villains have a Quirk eraser. Meanwhile, Eijiro chases the villain to a dead end. The villain uses his Quirk to create blades on his body but Kirishima knock the man down. In this situation, the villain injects himself with a Quirk booster, that allows him to generate unleashes a flurry of blades that consume the entire alleyway.
Red Riot tells all the bystanders to retreat. Even with his Hardening quirk, the blades break through his skin, sending Kirishima flying back. The villain arrogantly claims he'll be able to save his friends and sends multiple swords at Eijiro. Red Riot knows he has to protect everyone who hasn't gotten away yet. Remembering an advice Katsuki gave him, Eijiro hardens his body even further, revealing his new super move: Red Riot Unbreakable.
Thank to this, Kirishima breaks through his attacker's assault, breaking the many swords apart, and defeats him. The defeated man tries to escape but Fat Gum intercepts him and traps the villain inside his stomach. Fat Gum reminds Red Riot to always subdue a villain as quickly as possible and to never fall for their schemes.
Eijiro thanks Fat Gum for saving the day.The civilians thank Red Riot for saving them and they recognize he put himself in the way of the attacks to protect them. Fat Gum commends Red Riot for an epic debut and the bystanders say he will become a great hero one day. Fat Gum tells his sidekicks that Trigger is banned in Japan. Eijiro compliments Fat Gum for knowing his stuff and Suneater hides his face in his hood, embarrassed he couldn't be useful but Eijiro tries to encourage him. Fat Gum is worried about the existence of drugs that disable people's Quirks.
The next day at U.A in Class 1-A, Denki comments that Eijiro's Hero name, Red Riot, is on the Internet and his Hero debut in defeating the thug and saving civilians is also on the Internet.
A few days later, Eijiro along Izuku, Ochaco, Tsuyu and the Big Three, are heading out at Sir Nighteye's Office and see that many Heroes are gathered; Fat Gum; Eijiro and Tamaki's Internship mentor and Ryukyu; Ochaco, Tsuyu and Nejire's Internship mentor. Surprisingly, Shota and Gran Torino have also gathered. Thanks to the information all the Heroes provided him with, Sir Nighteye was able to make substantial progress with his investigation, of a organization named Shie Hassaikai; this captures Eijiro, Izuku, Ochaco and Tsuyu's attention.After Sir Nighteye and his sidekicks explain the situation regarding the organization and its relationship with drug trafficking, Fat Gum intervenes. He explains that he, Eijiro and Tamaki were involved the other day in a battle against a thug in which Tamaki was shot with a bullet that contains a drug that can damage the Quirk Factor, that allow a person to use his powers. Fat Gum follows up by explaining that thanks to Eijiro's brave actions by protecting Tamaki, they were able to obtain a bullet with the contents still inside. Fat Gum explains that after examining the contents of the bullet, they discovered that inside the bullet were human blood and cells, which disturbs the everyone.
Sir Nighteye states that Chisaki's Quirk and the Quirk-destroying bullet are related. He explains that Chisaki has a daughter that had no birth certificate and details about her are unknown. She says that Izuku and Mirio encountered her on their patrol and she had a number of bandages on her. Gran Torino comments that since they live in a superhuman society, anyone can do anything if they put their mind to it. Eijiro asks what Gran Torino means. Sir Nighteye explains that Chisaki is probably using his daughter to make those Quirk destroying bullets, which disgusts Eijiro, Ochaco and Tsuyu. Izuku and Mirio stand up and declare that this time they will definitely rescue Eri. Sir Nighteye states that their objective will be to save Chisaki's daughter.
With the meeting over, Izuku and Mirio explain to their classmates what occurred between them and Chisaki. Izuku and Mirio are still crestfallen for being unable to save Eri when she was right in their hands. Shota spots his Class 1-A students and talks to them about originally suspending their Internships since the League of Villains are involved. Before they start protesting, Shota gives them permission to take part in Eri's rescue operation and signifies his decision by fist bumping Izuku's chest.Finally, the day of the police raid on the Shie Hassaikai base begins. As they go through the operation, several comrades are left behind to face the threats, like Ryukyu's Team against Rikiya Katsukame or Tamaki against three of the Eight Expendables. In the underground labyrinth, Shota is attacked by a piece of manipulated wall, courtesy of Mimic, but Fat Gum shoves Shota out of the way, and is thrown into another room. As Fat Gum gets up, he is surprised to see that Eijiro is with him. Eijiro tells Fat Gum that he was also trying to protect Shota as well but once he did, he was swallowed by Fat Gum's Quirk.
Suddenly, two of the Eight Expendables, Kendo Rappa and Hekiji Tengai, appear. Eijiro activates his Red Riot Unbreakable. Rappa launches rapid bullet-like punches at great speed, striking Fat Gum and Eijiro. Fat Gum was able to mitigate the damages thanks to his Quirk, but Eijiro, although his super move also mitigate the impacts, sees that his arms are bleeding and becomes shocked that Rappa's punches managed to break through Red Riot Unbreakable's defenses. Fat Gum counters with a punch of his own, but is surprised that his punch strikes a barrier instead.The fight continues, and Rappa launches an assault on Fat Gum with his multiple fast punches, while Eijiro watches in disgrace as he is unable to do anything. Disheartened, Kirishima believes there's nothing he can do to help. Tengai sees Eijiro's fear and notes that the look in his eyes confirms he has accepted defeat. However, Eijiro appears in front of Rappa, which surprises Tengai. Eijiro is struck by Rappa's fierce punches and manages to withstand it, which takes Rappa by surprise.
As he falls to the ground, a bloody and beaten Eijiro states that his intervention was not meaningless as it has given Fat Gum the time needed to release his accumulated strength. Fat Gum, who is now shrunken and skinny yet muscular, reprimands Tengai for calling Eijiro's intervention meaningless. Thanks to Eijiro few seconds of bravery, Fat Gum has absorbed Rappa's accumulated blows which have in return given him great strength, and delivers a powerful punch that smashes both villains.
Surprisingly, Rappa managed to survive Fat Gum's powerful punch and is standing; but in a twist of events, Rappa tells Fat Gum that there are first aid supplies in a nearby room and tells him to treat Eijiro's wounds while referring him to as a man. Rappa has taken a personal interest in Eijiro and Fat Gum which is why he is helping them out. Rappa tells them to use the first aid supplies so that next time he can battle them again with their lives on the line.Neither Eijiro nor Fat Gum can continue participating in the rescue operation due to their injuries, which ends in success thanks to Izuku, who defeats Overhaul and rescues Eri. Later on Eijiro is seen being carried to the hospital after the mission was completed.
With the beginning of October, Izuku, Ochaco, Kirishima and Tsuyu were given permission to go to Sir Nighteye' funeral, along with the Big Three, All Might and Aizawa. His internship with Fat Gum was postponed.
Days later, Shota informs Class 1-A that U.A. is having a School Festival. Kirishima asks him if it's really okay to be so carefree at those times with the proliferation of villains. Shota tells him it's a good point, but explains that the festival is sponsored by the other departments such as the General Department. However, Shota points out that part of the festival will be within U.A. and tells Class 1-A to pick out a program to perform at the festival. After several deliberations, the entire Class 1-A decides that their school festival program will be a live performance and dance with party space.
Class A-1 students are divided into three groups, Band team, Dance team and Staging team, Kirishima is part of the latter. During the following weeks, the various teams practice their respective functions. When Mina tells Izuku what she means is he is being switched over to the Staging Team from the Dancing Team, to help maneuver Yuga during his part of the presentation. Eijiro joins in begging Izuku since there is a part in the play that he needs to care of as they say Izuku was selected since he and Yuga have been getting along. After Izuku accepts the change in position, Eijiro thanks him for agreeing.
On the appointed day, the performance of class 1-A ends up being a huge success.
As November comes to a close, at U.A. in the lounge, Shota reveals that Eri will be looked after by U.A. As Eijiro welcome Eri, Shota states that the decision for U.A. to look after her is because she does not have anyone who can take care of her and he is the only one who can prevent her Quirk from going out of control again. Mirio will also be helping Eri and welcomes Class 1-A to visit her once in a while since they will all be busy.
Then, Shota tells Izuku, Eijiro, Ochaco and Tsuyu to return to their dormitories as they will have visitors, resulting to be the Pussycats, who came to celebrate Ragdoll's reinstatement. Eijiro assumes that the Pussycats have returned so that they can rank higher in the JP Hero Billboard Chart, to which Ragdoll refutes and replies that they have returned due to their high approval ratings meaning that there are many fans who want to see them back in action. Eijiro cry some tears of joy for this.
At the U.A. dorms, Eijiro and his classmates watched a television report of a Nomu attack in the city and was horrified as it showed Endeavor being overwhelmed by the Nomu's attack. A worried Eijiro looked to Shoto who walked in to watch the scene of his injured father.
After Endeavor defeats High End stands up victorious, Shoto collapses to his knees, relieved his father is still alive. Kirishima is one of the classmates who approaches him to console him.
Kirishima participates in the first round of the Joint Training Battle. His teammates are Denki Kaminari, Hitoshi Shinso from Class 1-C, and Tsuyu Asui, who leads Class 1-A team. Their rivals of Class 1-B team are Ibara Shiozaki, Kosei Tsuburaba, Hiryu Rin, and Jurota Shishida.
Before the match stars, they spend to much time learning about Hitoshi's Brainwashing Quirk. When the match begins, they didn't get to form a proper plan. They decide that regardless, they'll have to fight to win. Thanks to his Quirk, Koji tell Kirishima that Ibara is alone, spreading her vines out. Class 1-A takes the bait and heads toward her position but they walk right into a trap. Jurota, with Kosei on his back, suddenly rushes in with his Quirk activated and smashes both Eijiro and Tsuyu through nearby pipes with Roaring Rage. After a short scuffle, Hitoshi manage to stop Jurota with his Quirk.
During the following skirmish, Tsuyu Asui managed to capture Kosei with her tongue, and takes him back to the jail to eliminate him from the match, being persecuted by Jurota. Eijiro and Koji trying to block his path, but Jurota quickly transforms back to a human to squeeze between them, and then back to his beast form. Jurota tosses Eijiro into the air, allowing Ibara to capture him with her Vines and lock him in prison, along with Koji who had also been captured.
Despite the capture of Kirishima and Koji, the Class 1-A team manages to achieve the victory. Shota asks the victorious Class 1-A team to reflect on the match and what they have learned. Kirishima says that his Quirk is difficult to utilize in a situation where a fight is trying to be avoided, and knows he needs to be able to apply his skills outside of combat. Shota tells Eijiro to learn how to set up situations for close combat.
Eijiro rejoins Fat Gum for his internship.