My Hero Academia uses the term "My hero" in more than one way. Superstars like All Might can always save the day and inspire the crowds with their power and glory, but in many cases, the noblest heroes are those who can personally inspire a single person to become their best selves. For example, Izuku is a personal hero to Ochaco and for someone else, Mina Ashido is a hero like that, too.
Even if Mina is only a middle-of-the-road trainee hero at the prestigious U.A., she has the heart of a champion, and one fateful day, she inspired her middle school classmate Eijiro Kirishima to take another look at himself and decide once and for all if he's ready to become a hero, too.
Mina Sets A Heroic Example For Kirishima
Eijiro knew Mina before they enrolled at U.A. since they attended the same private middle school together. At the time, Eijiro had self-doubts because of his "boring" and unremarkable Quirk, one that only hardened his skin somewhat. He felt invisible and unworthy to become a hero, but he did have a classmate of interest: Mina Ashido, from class 4.
Eijiro once saw her chase off some bullies who were trying to pressure a meek classmate into abusing his Quirk to counterfeit money, and Eijiro saw something remarkable in her. Later, on the street, Eijiro witnessed Mina stand up to a huge, terrifying villain and protect her classmates, then fool the villain into turning himself in to the local police. Mina didn't act without fear; she acted in spite of it, and because of this strong will, Mina applied to the famed U.A. Few, if any other students in that middle school were applying to such a prestigious high school.
Eijiro knew that he couldn't afford to fall behind. He already had a role model in the pro hero Crimson Riot, and Crimson Riot echoed Mina's words when he said that he acts despite his fear, not with a lack of it. To Crimson Riot and Mina, being strong of heart meant facing and overcoming fear, while being humbled by it at the same time. Anyone who arrogantly thinks they're immune to fear is in for a lot of trouble, and their vanity will turn on them. So, Eijiro made up his mind that he would find something worth risking his life for.
Kirishima Works Hard to Catch Up to Mina
Over the next few months, Eijiro put Mina on a pedestal and thought of her as a rival of sorts, without actually telling her as much. He wasn't close to her as a friend, but he knew what she was capable of. His relationship with her was along the lines of "you showed me up this time, but next time, I'll be the hero!"
Eijiro struggled with self-doubt for years and resented his Quirk. Now, he was ready to face his own fears and grow stronger and braver from them, just like Mina. He even changed his choice of high school to U.A., gambling that he would reach for the stars like his personal hero was aspiring to do. Applying to a school like U.A. takes guts, and the old Eijiro wouldn't have bothered; however, he couldn't let Mina show him up again.
Mina finally realized what was going on when she met Eijiro just before their first semester at U.A. -- after they both had been accepted as first years. Mina was surprised but amused, too, noting that Eijiro had changed his hair to make horns like hers, and it was red to match that of Crimson Riot's.
Eijiro had two heroes to live up to by now, and he wasn't afraid to show it. Mina acknowledged that it couldn't have been easy for Eijiro to watch her be brave while he was a helpless bystander, but Eijiro was over it, and he was looking forwards, not backward. His new rivalry was pushing him in one direction, and Mina proved she was aware of this one-sided rivalry by asking Eijiro to tell her when he had cleared away his doubts and fears 100 percent.
Even if the Eijiro/Mina rivalry has yet to match the intensity of Izuku/Bakugo, Mina is no doubt thrilled to see Ejiro working so hard to catch up, and it may motivate her to push herself harder, too; to make sure she doesn't fall behind or let Eijiro down. She is someone's personal hero, and that means being her own personal best. She and Eijiro can walk forward together side by side.