Inko is Izuku's mother, and she cares deeply for Izuku, even when her son was initially Quirkless; she apologized profusely as if it were her fault. It is hinted she took her sadness on herself and gained more weight because of this, but it is unknown if this really true.
However, once he developed a quirk and got into his dream school, she was happy he got powers but felt guilty about her former beliefs, and after she saw it in a drawing she even made a costume for him herself. She brought up her past actions and apologized for not believing that he could be a hero. She soon told him that she would support him all the way until he accomplished his dream as Izuku was touched at this and thanked her for her words.
She later showed that she was worried about the consequences of her his new Quirk after seeing the damage done to his body. Indeed, after the ordeal at the training camp, Inko was completely against him resuming his studies at U.A., due to their inability to properly protect her son. Izuku was shocked at this and couldn't say much to his mother's firm stance. Only after Izuku showed her Kota's letter as a sign he was becoming a hero did she change her mind about U.A. She also made All Might promise to take care of him, and stay alive for him.
While upgrading his costume, Izuku only added a few things on it and refused to modify it even further as he was attached to it because he recalled his mother had made it for him.
Izuku has always admired All Might ever since he was a small child and wanted to be a hero just like him. In their first meeting, All Might saved Izuku from Sludge Villain and signed a happy Izuku's notebook. However, Izuku was very shocked to see All Might's true form and was dismayed when the latter told him being powerless wouldn't help him be a hero. Despite that, Izuku earned All Might's respect after he ran toward the slime monster trying to save Katsuki, a mentor-student relationship bloomed between them and All Might chose him as his successor. While All Might's training on Izuku was rough, the latter continued to give it his all. They grew closer as All Might listened to his resolve of training and doing more than he has to become a great hero, impressing the hero.
All Might is Izuku's confidante, mentor, friend in and out of school, and they share a mutual respect for each other's heroism ideals. All Might returned this by telling Izuku that he was formerly Quirkless before he got One For All. All Might was also impressed by Izuku improving on his quirk after his time with Gran Torino and deemed it was time to tell Izuku of his Quirk's history. 
Izuku's admiration and respect for All Might is so great that he avoided trying to attack All Might during the End of Term Test, but when he had no choice but to attack All Might with Katsuki's Grenade Bracer, Izuku apologized in advance.
At first, Izuku was an extreme fanatic who tried to imitate All Might from his style of name and costume design. As he matured later on, Izuku slowly learned to become his own hero and develop his own style. This change was noticed by All Might who was proud to see Izuku on his way of becoming his own hero and improving in his skill.
Izuku and Katsuki have known each other since early childhood, but their relationship has deteriorated over the years (though interestingly enough, Izuku continues to call Katsuki by his childhood nickname, "Kacchan"). Ever since failing to develop a Quirk as a child, while Katsuki developed his, the latter has always seen Izuku as weak and bullied him, giving him the derogatory nickname “Deku” which he always calls him.
Izuku later surprised Katsuki by trying to save him from the Sludge Villain. Much later, Katsuki caught up with him and berated him for his actions, calling him a Quirkless failure most likely out of pride. Izuku's heroic act is also what caused All Might to choose him as his successor of One For All, thus making Katsuki indirectly responsible for his acceptance into U.A.
Izuku later stood up to Katsuki and enrolled in U.A. High School. He also revealed his new quirk, with Katsuki reacting in surprise as the latter angrily questioned if Izuku was intentionally hiding his powers from him for years. In a training battle, Katsuki attacked Izuku but once again Izuku surprised Katsuki by revealing he has been memorizing his moves and knew of ways to counter them as he once possessed a strategy book that detailed all of Katsuki and other's moves before Katsuki had burned it. Finally standing his ground against Katsuki, Izuku tells him that he is no longer the same kid Katsuki used to bully even stating he will use the nickname Katsuki gave him as inspiration. Enraged by Izuku's bold claims, Katsuki attacked relentlessly to get him to use his quirk which worked but ended with Izuku defeating him for once. After the exercise, Izuku caught up to Katsuki and told him he obtained his powers from someone else but Katsuki does not believe it and swore to defeat him.
Izuku states that Katsuki makes all of Izuku's insecurities about himself bubble to the surface. Despite the two having such a strained relationship, Izuku still admires him for his strong quirk, natural combat capabilities, confidence, and his ability to win. Ever since the end of the Battle Trial Arc, Izuku has not spoken to Katsuki on friendly terms due to Katsuki considering Izuku his arch-rival. Even still, Izuku still has respect for Katsuki and is still shown to care for him, as shown when he was trying to ensure Katsuki was safe from the villain attack but Katsuki was captured by the Vanguard Action Squad, Izuku used all his strength in an attempt to save him and spiraled into despair after he failed to do so. Directly after, Izuku teams up with Tenya, Ejirou, Shoto, and Momo in an attempt to rescue Katsuki from the League of Villains' hideout.
Back at U.A. sometime later, Katsuki remarked to Izuku was really making his power his, revealing he believed Izuku's story of borrowed quirk, which worried Izuku.
Later on, Katsuki and Izuku take out their stress on each other in an emotional fight, which Katsuki wins. After the fight, Katsuki learned the full truth of Izuku's quirk and his connection to All Might which he seems to understand and kept the secret to himself.
Since the fight, the two better understand each other and have become more reminiscent to that of a proper "friendly" rivalry, although they still have a long way to go.
Ochaco was the first person that Izuku interacted with when he first came to U.A. High. He saved her from being attacked by giant robot and she did the same by ensuring he landed safely on the ground. The two met again after becoming classmates and soon became best friends; they get along very well and their discussions are always bright and friendly. Ochaco was the one that turned his once demeaning nickname "Deku" into a positive identity for him, when she said it gave her a "never gives up“ vibe. They share similar ways of quick thinking, which contributes to their friendship.
They mutually respect each other as Izuku defended her to Katsuki Bakugo and Camie, thinking of her as a brave and resourceful person by herself. Ochaco is inspired by him, striving for his level of tenacity and perseverance. They are protective of one another as Ochaco quickly called the police after she found Izuku threatened by Tomura Shigaraki.
Earlier on in the story Izuku was not able to hold a conversation with her as he got embarrassed whenever he spoke to a girl but as he got to know her more he was able to speak confidently with her.
It has been hinted throughout the series that Izuku harbors feelings for Ochako, though it has not yet to be confirmed. However, it has been confirmed that she has feelings for him.
In their first meeting, Tenya labeled Izuku's muttering about heroes as a distraction and thought he would be a hindrance to the school which earned Izuku bad attention from his peers. However, in the entrance tests, Izuku surprised Tenya by selflessly going back to save Ochaco Uraraka and using his Quirk to destroy a giant robot in the process.
When they met again in class, Izuku first thought that Tenya was scary and that they wouldn't get along, but was surprised as the latter apologized for his previous treatment to him and even considered Izuku better than him in many ways after the entrance course, much to Izuku's shock. Izuku got to know Tenya better, where he found out that while the latter was serious he was also kind and they ended up becoming friends. Izuku and Tenya are usually friendly with each other. However, sometimes their friendship slightly falters such as when Izuku criticized Tenya for seeking revenge against Stain and Tenya punching Izuku in the face for acting recklessly by attempting to save Katsuki.
Despite this, Izuku and Tenya's friendship has rebounded back many times despite these mishaps, mainly because they are only concerned for each other's well being. They are usually seen together having friendly discussions. Izuku resigned as Class President and named Tenya as his successor, knowing that he has better leadership qualities than him. After Tenya was defeated by Shoto, Izuku was saddened to see his friend lose. Since Izuku knew that Tenya has a grudge against Stain, he tries to save him from his death. While recuperating at Hosu General Hospital, both Izuku and Tenya resolve to become stronger together.
Shoto saw Izuku as his arch-rival, due to him having connections with All Might (a person with whom his father has a major rivalry). Izuku, on the other hand, has a lot of respect for Shoto, admitting that he is a far stronger than him. Shoto confronted Izuku at the festival asking if he is All Might's secret child but the latter denied this as Shoto decided to reveal his family history. After hearing Shoto's tragic backstory and seeing his sadness, Izuku started to show sympathy for his pain and resolved to help him overcome his dark past by getting him to use his power, telling Shoto that the power is his own and not his father‘s. Although Izuku lost to Shoto while trying to help him, Izuku's actions did have an impact, as Shoto stopped rejecting his power.
Shoto even came to his aid when Izuku and Tenya Iida were attacked by Stain and they worked well together even defeating the infamous hero killer. After the battle, Izuku and Shoto are on friendly terms with each other, with Izuku even laughing at Shoto's expense when he was worried that he tends to hurt people's hands.
Shota is Izuku's homeroom teacher. Initially, Izuku did not recognize him until he used his quirk to restrain him, which caused Izuku to remember he was Eraser Head, a hero that he respected. Initially, Shota firmly did not believe Izuku could be a hero, due to his reckless behavior when using his Quirk as he would be useless in battle if he kept getting injured. However, Izuku proved to Shota that he has potential and did not expel him. Throughout the series, their relationship can be defined as a rocky, troublesome student-teacher relationship. As his teacher, Izuku listens to Shota's orders and advise in order to improve himself. He has some level of respect towards Shota, as he was surprised at the latter handling several villains by himself. However, Shota's cold and logical personality conflicts with Izuku's personality and mindset, making it difficult for the two to get along. Out of all his students (besides Katsuki), Shota appears to antagonize Izuku the most whenever he does something that upsets him, a recurring problem being Izuku overusing his Quirk and breaking his body. As such, Shota refers Izuku as the 'Problem Child'.
However, Shota is still Izuku's teacher and as such, ultimately cares for him. He would offer some level of consolidation and guidance for Izuku when he is upset, and he will make sure Izuku does not do anything dangerous and act upon it. In return, Izuku once tried to help Shota when he decided to fight off several members of the League of Villains and was amazed by the latter's abilities, since he realized he underestimated him. However, he was horrified to watch him being overpowered by Nomu. This shows the more caring and inspirational side of Shota helps Izuku get along better with him. Izuku also carried his teacher to safety after All Might appeared.
It is possible another reason they sometimes do not get along well is because of Izuku's personality and mindset bearing similarity to All Might's, who Izuku looks up to. Shota and All Might do not get along, and this is extremely evident in Shota and Izuku’s relationship.
Due to them being groomed to be the successors of their respective mentors, Izuku and Tomura mutually despise each other; Tomura despises Izuku for his admiration of All Might (someone he hates) while Izuku doesn't agree with Tomura's villainous actions. During USJ, Izuku saved All Might, which caused Tomura to take an interest in Izuku as shown when he watched Izuku's match during U.A.'s Sports Festival.
Later in Kiyashi Ward Shopping Mall (Wookiees), they unintentionally met each other again, so Tomura decided to talk with Izuku about the difference between him and Stain. After hearing Izuku's thoughts on the matter and before leaving the shopping mall, Tomura declared that the next time they met, he would show Izuku no mercy.
Tsuyu respects Midoriya for his heroic actions, as well as his victory against Katsuki. She becomes friendly with Izuku, requesting he call her by her first name, which is something he frequently forgets and she corrects him though he sometimes remembers. She even noticed the similarities between Izuku and All Might's powers which worried him until she gets a vague answer.
During the Unforeseen Simulation Joint Arc, she saves him from being attacked underwater and they worked together well against their enemies. In turn, Izuku also tried to save her from being attacked by Tomura Shigaraki but failed, though they were saved by Eraserhead and All Might. In Rescue Trial Arc, she was receptive of Midoriya's plan to subdue the swimming villains, showing not only respect but also trust. After Shoto defeated Izuku in the Sports Festival, Tsuyu was one of the few students who went to Recovery Girl's office to see if he was fine or not.
Their friendship is built on a mutual respect towards each other. They teamed up along with Ochaco and Mei Hatsume during the Human Cavalry Battle. Fumikage respects Izuku as a leader, as he leaves him with making the decisions of their team. Izuku himself respects Fumikage's strength and the power of his Quirk, acknowledging him as one of the strongest combatants in Class 1-A. They later sat beside each other to watch the sports festival tournament. Izuku later cheered on Fumikage and Tsuyu during their Exam against Ectoplasm.
During the training camp, Izuku along with Mezo Shoji resolved to save Fumikage from his rampaging Dark Shadow in which they eventually succeeded. After Fumikage is kidnapped by Mr. Compress, Izuku chased after the villain in order to save Fumikage as well as Bakugo. After Bakugo was captured, Fumikage tried to comfort Izuku.
Izuku is on good terms with Eijiro, as in the Unforeseen Simulation Joint Arc, when Izuku was wounded from trying to help All Might with Tomura Shigaraki, Eijiro tried to help him. Izuku was thankful though worried the latter would discover All Might's secret but Ken Ishiyama intervened.
In U.A. Sports Festival Arc, when Shoto told Izuku that he will defeat him, Eijiro tried to stop them from any further arguing after Izuku started to talk negatively about himself, Eijiro tried to encourage him. Eijiro also told Izuku that he is envious of his Quirk.
Eijiro seems to admire Izuku's growing confidence and seems to be impressed by his quick thinking and logical reasoning. He also seems capable of understanding Izuku's feelings to some extent, understanding how he felt when he was unable to rescue Katsuki. Eijiro also asked Izuku to help him in his plans to rescue Katsuki from the League of Villains. Izuku respects Eijiro by admiring his determination and he was aware of the bond Eijiro shares with Katsuki, which gave him an idea for Eijiro to be the one to retrieve him.
In the Internship Arc, Eijiro and Izuku are shown to be on even better terms than previously, often interacting in friendly ways. They later worked together in saving Katsuki Bakugo from the League of Villains and were successful.
The two first met at the entrance exams where Aoyama saved Izuku from being attacked by a robot, though he did this for points as he remarked that the latter made good bait and he would most likely not see him again. Izuku later excelled in the exams and became classmates with Aoyama. It was shown his opinion had not changed, as he remarked on Izuku's lack of skill to Ochaco. However, Izuku surprised him with his powerful quirk which allowed him to remain in the school.
After this, the two had no further interaction that was notable until the Remedial Course Arc. Aoyama would act strangely around Izuku who would note that he could never get a good read off the latter. Izuku is later scared when Aoyama spied on him as he slept and left a message (in cheese) to say he knows Izuku's secret, which left Izuku wondering if Aoyama is aware of his secret. In training, Izuku is called out to by Aoyama and is shown one of his new moves though it causes him severe stomach problems. Seeing him in this state, Izuku took Aoyama away to recuperate before he asks him what he meant in his message. Aoyama explained that he is aware of Izuku not being accustomed to his quirk and reveals that he went through a similar experience and compared his powers leaking out in his childhood out to Izuku's initial lack of control of his own quirk before they both overcame it. He then tells Izuku that he is not alone in hardships, as it is better to face them together or they won't excel. His words relieve and cause Izuku to smile and thank him for his support. After a few days, Izuku and Aoyama became good friends with some of the class noting on their frequent interaction.
During the School Festival, Izuku is tasked with securing Aoyama as the disco ball since the class knew of their bond.
Izuku gets along very well with Minoru, though like most of his classmates, he is put off and disgusted by Minoru’s perversions but admires his heroism and quick thinking in difficult times. In turn, Minoru has come to admire Izuku for his acts of heroism and for believing in his abilities as a hero, although he is somewhat skeptical at first of Izuku's determination. The two have become friends, particularly following their battle together against the Villain Alliance.
They get along well though Mashirao didn't team up with him since Izuku was a target in U.A. Sports Festival Arc. Despite that Mashirao tried to warn him about Hitoshi Shinso, Izuku also stood up for him after Shinso insulted him. Mashirao worried for him but was relieved he emerged from the fight victorious.
During the Vs. Hero Killer Arc, he was very amazed that Izuku improved on his quirk and overcame his drawbacks.
He also tried to comfort Izuku at the training camp after he was the only one left without a partner.
The two have had little interaction but are on good terms and have respect for each other. Shoji saved Izuku twice during the school trip first from a rampaging Dark Shadow and than from Himiko Toga. Shoji trusts Izuku, as he was willing to lead the out of control Dark Shadow towards where Todoroki and Bakugou were despite the danger it placed him in. Shoji Also carried an injured Izuku throughout the attack during the training camp.
Despite their efforts they failed to save Katsuki resulting in Izuku breaking down. Along with Tokoyomi, Shoji tried to comfort Midoriya on their loss. Later he visited Midoriya in the hospital with the rest of the class.
They are classmates of Class 1-A and were both voted as the Class reps, however their partnership did not last long due to Midoriya stepping down for Iida. Midoriya along with Iida and Yaoyorozu would later join Kirishima and Todoroki to rescue Bakugo. Due to the group's teamwork they were successful. Both are also friends of Todoroki and were seen showing concern for him after he failed the Provisional Licence Exam.
Mei and Izuku first met during the U.A. Sports Festival Arc. Mei took a quick interest in Izuku when he got first place in the Obstacle course and as a result, got the ten million point headband. She saw this as an opportunity to bring attention to her inventions by using Izuku and approached him before the Human Calvary Battle. In return for joining his team, she offered him and the other teammates support equipment to aid for their battle. Her tendency to get in his personal space creeped Izuku out but they got along better because of their shared admiration for heroes.
After the U.A. Tournament, the two would not meet again until Izuku wanted Power Loader's help in improving and redesigning his costume. Mei recognized him during their second encounter, but didn't remember his name and dismissed it in order to go back to her inventions only to return her attention back to him when he brought up his purpose for entering the workshop. She provided Izuku some options for improvements on his costume and created Izuku's Costume Gamma.
Overall, the two generally get along well as Izuku has no problem talking with Mei during their first encounter. They got acquainted over a jetpack Mei created that was similar to a hero Izuku was familiar with. Izuku appears to tolerate Mei more than some of his classmates, like Tenya and Ochaco since he shares some similarities to her as he creates ways to counter the quirks of others and rambles as she does the same about gadgets.
It is shown that while still having trouble training, he goes to see her for a new gadget that might help him progress with his powers. She has gotten use to him as she now remembers his last name, in contrast to her old mistake. Izuku is still friendly to her though he is put off by her habit of getting in his personal space.
Mei later gives Izuku new mechanical gloves that he asked for. She handed him the instruction manual for them before running off after he thanks her.
Mei's invention came in handy as Izuku used them to defeat the villain Gentle Criminal.
At first, Izuku was largely put off by Mirio, due to the unusual nature of their first encounter. Furthermore, Izuku was skeptical of Mirio's status as one of the "Big Three" at U.A., due to Mirio's subpar performance in the sports festival the previous year. This changed after Mirio gave an excellent demonstration and explanation of his quirk and fighting technique, after which Izuku grew to have a great amount of admiration for him, even commenting that Mirio talks just like a Pro Hero already. Izuku's respect grew upon learning that Mirio was one of the originally proposed candidates for inheriting One For All. Though sometimes still a bit off-put by Mirio's intense amiability and enthusiasm, Izuku and Mirio get along very well and are very similar in terms of heroic ideals. Mirio put in a good word about Izuku with Sir Nighteye, and the two have been working together in an internship since.
He was visibly disturbed when he learned that Mirio's Quirk was forever lost from Chisaki, and expressed anger towards Chisaki for that.
After Nighteye's death, when Izuku saw how optimistic Mirio was, Izuku went as far as to propose that Mirio could take Izuku's Quirk, indicating how Izuku believes that Mirio is truly the worthier candidate for One for All, like Nighteye had said. However, Mirio turned it down as he had faith that Eri might master her quirk to restore his and believed in the words of Nighteye of being a hero.
Izuku was impressed by this and accepted Mirio's determination and it seems they became friends afterwards. The two get along and Izuku still looks up to Mirio for maintaining a smile in spite of his situation, which is something All Might did in the face of adversity.
At first, Kota despised Izuku and Class 1-A for always working so hard to better themselves against fighting villains. He even went as far as hitting Izuku in the crotch for trying to be friendly towards him, as he voiced his dislike of heroes. In spite of this, Izuku tried to get along with Kota, due to their similar circumstances of both being "quirkless" (Izuku not originally being born with a Quirk and Kota refusing to use his quirk). Though he had no luck due to a disagreement in their ideals. Because of his past, Kota ignored anything that dealt with heroes and villains, and even Quirks altogether. After finding his secret hideout, Izuku tried talking to Kota only to have him snap at him because he's never gone through what he has.
However, Izuku saved Kota from the Muscle Augmentation villain (who is also the one who killed Kota's parents) after realizing he was in danger. When Kota asked why Izuku took it upon himself to save him especially by how he treated him, Izuku stated he had seen the latter was in danger and he had to save him. Izuku shielded Kota from the Muscle Augmentation villain at all costs, even going past his limitations.
During the battle, Kota used his Quirk out of desperation in an attempt to help Izuku. From this, it is shown Kota gained respect for Izuku. After the battle, he tells Kota that his parents died to protect him and says he risked his life for him because he wanted his acknowledgment as a hero. Izuku then tells Kota to help save others just as he helped save him.
At the hospital, Izuku soon got a letter from Kota, who apologized for his treatment towards him and thanked him for saving his life. Izuku later used the letter to show All Might and his mother that he was well on his way of being a hero after having an effect on someone.
They met again when the Pussycats visited U.A., Izuku was happy to see him and thanked him for the letter. Shino soon pointed Izuku out to the new shoes Kota has, which looked exactly like Izuku's shoes. Kota became embarrassed after Izuku pointed out the match. 
Izuku and Eri never fully interacted, but the short time they had with one another built a powerful bond between the two. When Izuku first encountered Eri, seeing the bandages she had, as well as how fearful she was towards Chisaki, he tried to protect her from Chisaki until he was forced to let her go back. After learning how Eri was being experimented on by having Quirk-erasing bullets manufactured from her body, Izuku was horrified by the act and angered at himself for letting her go back to that. Aizawa even deduced that Izuku was going to act recklessly to try and save her even if he tried to stop him, which Izuku didn't deny.
When they finally reunited in the battle against Chisaki, Izuku immediately followed orders to try and rescue Eri, and even pushed himself to use One for All 20% to protect Eri and defeat Chisaki. Even though he was beaten down by Chisaki afterwards, and Eri came back to Chisaki declaring that Izuku cannot save her, and this was not his business, Izuku declared that because Eri was crying, he would save her no matter what.
After taking Eri from Chisaki, Izuku tells Eri that he will not let go of her again. When he experiences her Quirk being used, and being told how dangerous it is to be with Eri, Izuku still refuses to let Eri go, explaining that because of how her Quirk has reverted the damage he has done to himself using 100% before he could even feel pain, he states that Eri possesses a "kind, gentle Quirk", something that drives Eri to tears. This also makes Izuku go as far to use One For All: Full Cowl - 100%, something that would destroy his entire body at blinding speed, to make use of Eri's Quirk, and asks her to lend him her strength.
After the battle is over and they are in the hospital, despite Izuku being discharged, he wants to stay by Eri's side until she wakes up, but is convinced by Shota to go back..
Izuku later met her again and is able to properly introduce himself to her. He and Mirio invite her to the Cultural Festival to have fun after noticing she is still haunted by Chisaki's influence.
When she arrives at U.A., he is excited to see her and promises to perform for her on stage.
Izuku was intent on fulfilling his promise as he prevented Gentle Criminal from attacking the school and fought the villain by himself. Izuku later performed on stage and caught a glimpse of Eri smiling and was pleased at his success.
Gran Torino requested Izuku to be his sidekick in an internship so that he can properly teach Izuku about the One for All Quirk. Gran Torino and Izuku were off to a bad start when they first met, with Gran Torino putting up a facade of being senile and Izuku being disappointed with having to train with someone who was no longer functional. However, when Izuku moved to leave Gran Torino promptly dropped his facade and showed Izuku what he was really capable of as Izuku was amazed by his true nature. He saw the similarities between All Might and Torino's personality shifts which helped him understand their connection. He started to gain respect for Gran Torino, politely calling the elderly Hero Mr. Torino. They bonded to an extent and Torino's teaching helped Izuku gain better control of his quirk without hurting himself. Torino also protected Izuku from a Nomu while Izuku was worried for him.
Gran Torino has shown to be impressed with Izuku, stating that All Might chose a fine successor, due to Izuku's quick thinking and potential. As they parted ways, Gran Torino asked him his and Izuku replied it was Deku, with Torino becoming the second person to make Izuku proud of his nickname.
Izuku was very surprised to hear that All Might had a sidekick from Gran Torino. In their first meeting, he was intimidated by Sir Nighteye. The two were mostly at odds due to Sir's cold nature and skepticism of Izuku being the next Symbol of Peace. However, they both realized they were huge fans of All Might, with both having extensive knowledge of him as well as extensive collections of merchandise. Sir hired Izuku as an intern, and Izuku has been working since then to prove his worth to him.
After learning more about All Might's relationship with Nighteye, Izuku wanted to make the two meet so they can reconcile. Though Izuku wasn't able to find the time to bring it up due to the rescue mission for Eri, he got to tell him after the recuse was complete and Nighteye was taken to the hospital.
Izuku was horrified when he learned that Nighteye was going to die, and pleaded to him to keep hanging on, and cried for him as he died but not before Nighteye gave Izuku his blessing as All Might's successor.
Despite how Nighteye praised Izuku for being able to change the future, giving him hope for once, Izuku ultimately believed that Nighteye was right about Mirio being the worthier heir for One for All and even tried to pass it onto Mirio, but was rejected. Izuku also decided to live to Nighteye's expectations as a way to honor his memory.
Recovery Girl is one of the few people who know about Izuku's Quirk. Often, she scolds Izuku for using his Quirk dangerously, as he consistently requires her healing quirk.
Her scolding finally reached a tipping point, where she flat out says she will no longer heal his self-inflicted Quirk injuries after the Sports Festival, fearing that he will continue to cause serious harm to himself as long as he thinks he can just be healed by her.
Stain respects Izuku's reasoning to be a Hero and sees worth in letting Izuku live. Izuku, on the other hand, saved Tenya from Stain after intervening in the man's attempt to kill his friend. Izuku impressed Stain with his will to defend his friend and efforts to defeat him, which was something he deemed worthy as a hero. With the help of Tenya and Shoto Todoroki, Izuku managed to defeat the villain.
Also, when Izuku was captured by one of the Noumu-like creatures, Stain was the one who saved him as the latter expressed shock at this act and was scared at Stain's speech before he fell unconscious. While Izuku does not approve of Stain's nihilistic methods, Izuku respects Stain for living according to his ideals and never giving up on achieving his ideal world.
Because of their encounter, Shuichi Iguchi prevented his comrade Magne from killing Izuku declaring that he was the person that Stain saw fit to save thus being a man worthy of the title of a true hero.
Himiko first encounters Izuku when the Vanguard Action Squad attacks Classes 1-A and 1-B's field training. Himiko jumps him and briefly introduces herself before she is pushed away by Mezo Shoji. Unbeknownst to Izuku, the two meet again during the Hero License Exam where Izuku believes her to be Camie Utsushimi, a student from Shiketsu High School. This encounter only raises Himiko's interest in the boy, as she notes that their interest in each other seemed to be mutual. Izuku is surprised by her fighting abilities but finds her to be a somewhat scary person the more she interacts with him.
Being saved and carried to safety in a princess carry by her love interest, Himiko found out that the boy would save somebody even if that person was his opponent. Revealing her quirk to him but not her real identity, she was curious about how far his good will reached. During the Second Exam of the Provisional Hero License Exam begun, Izuku acknowledged her wishing of good luck to him.
After the License Exam, Izuku wanted to talk to her again about her stealth techniques but he was disappointed when he found out she had already left.
During Eri's rescue operation, he ran across her yet again when a disguised Himiko lovingly tried to cut him with her knife. Her quirk was deactivated by Aizawa and her identity revealed giving Izuku a shock as he was saved by his teacher. Putting two and two together, Izuku figured out that Himiko was likely the same girl that he had sparred with during the license exam.
Izuku first saw him on the internet and was confused by his crimes even wondering about his intentions.
Izuku unintentionally met him in person after accidentally bumping into him. Initially, Izuku did not recognize him until he heard his voice and remembered his habits. Izuku begged Gentle not to attack the festival as the villain saw Izuku as an obstacle that had to be removed, but after learning that he was a student of U.A high school he developed an interest in him.
As they fought more, Izuku was knocked down many times but wanted to honor his promise to Eri. His tenacity caused Gentle to gain a begrudging respect for him and steadily confined him more of his past. After he lost the match and of hearing of Izuku's dream, he treated the boy as an equal and told him to keep moving forward. Izuku still treated him like a threat and remained hostile to him however, the more they fought and hearing of Tobita's past, he treated him with more respect and care even stating he wouldn't laugh at his ambitions.
After defeating Gentle, he remained worried about him, even after being blasted into the air by him.
Gentle is the first villain Izuku defeated on his own and after he just got his hero provisional license.
They first met in the fighting tournament of the Sports Festival. Izuku learned much about Hitoshi's Quirk from Mashirao Ojiro but accidentally played into Hitoshi's hands, though the powers of those who previously wielded One For All freed him from Hitoshi's control. Hitoshi was shocked by this and tried to control Izuku again by claiming to be jealous of Izuku's Quirk, as it gives him combat efficiency.
On the other hand, Izuku ignored him though internally understood Hitoshi's situation as he himself was considered unfavorable due to having no Quirk. Before their battle in the Sports Festival, Hitoshi and Izuku were hostile to each other, but after their battle, Hitoshi seems to have gained respect for Izuku, telling him not to lose too pitifully while Izuku respects Hitoshi's goal to enter the Department of Heroics.