One of the many recurring themes in My Hero Academia is that even heroes have their own personal heroes, and the villains might feel the same way about their own role models. This can spur a trainee hero or a new villain to great heights, while other characters seem to be fending for themselves. One such character is Mina Ashido, the acid girl of the U.A. school's class 1-A.
So far, Mina has acted as middle ground when it comes to student heroes in the series, having a moderately powerful Quirk and the skills to use it. However, she's lacking a few key ingredients that have put Izuku Midoriya, Katsuki Bakugo and Ochaco Uraraka on the path to greatness.
The Control Group
So far in the series, a handful of characters, including Mina, have acted as a contrast to the more prominent characters. Some of the students at U.A. are more motivated, have superior Quirks or simply have more guts and grit. The best example is Izuku Midoriya, the show's protagonist, who was born Quirkless and has been making up for it in all kinds of ways, entirely on his own volition. Then, he met All Might in his true (and skinny) form, and resolved to become a great hero and a worthy successor to All Might, or die trying (and that might be literal). From that point on, Izuku's personal arc involved big risks, lofty ambitions, incredible courage and grit, and putting in more practice than any other student. Tenya Iida had his brother Tensei as a role model, and pushed himself hard, possibly too hard, to emulate him.
Mina, by contrast, is a more middle-of-the-road character and trainee hero, one who's adequate for the job but no more or less so far. That isn't a critique of Mina's character -- without characters like her, everyone would be high-strung and intense like Izuku, Bakugo and Shoto Todoroki, and and it would be tiring to have a show entirely made up of such characters. Contrast is needed, and Mina is there to act as a stablizing element to balance these intense main characters, and act as a control group for them.
What does a "normal" U.A. student look like? Mina Ashido, and a few of her other classmates, answer this question well. Her easygoing, fun-loving personality, lack of intense ambition and moderately powerful Quirk act as an example for the school's average students and allow the main characters to stand out even more. Mina doesn't seem too upset about this status quo, either. She's not aching with envy as she watches Shoto and Izuku reach for the stars, but is comfortable with her lot in life.
My Own Hero
Mina's motivation to become a hero makes her a fine foil to Izuku and Ochaco, who are intensely driven by their own role models. Izuku has All Might as his mentor and personal role model, and Ochaco has Izuku as her role model and hero. Mina Ashido, meanwhile, has no such figure in her life. So far, it seems she does not need one, either. One of Eijiro Kirishima's flashbacks recalled a time in middle school when Mina stood up to a large villain despite her fears, and she tricked him into turning himself in to the police. Eijiro and Mina's classmates all looked up to Mina, what with her street smarts and courage and useful Quirk. She was the role model, instead of having one, and she didn't let it go to her head.
This provides a much-needed contrast with characters like Izuku, Ochaco and Shoto, who all have someone to either live up to or prove wrong. Not everyone needs to have such a complex backstory, and it's refreshing to have a student hero like Mina who is dedicated to the way of the hero simply because they want to. Enthusiasm and courage are Mina's greatest assets, and for some characters, that is enough.
That personal arc does put some limits on Mina. She has only moderately powerful combat abilities and book smarts. Without a strong motivator, Mina will remain a middle-of-the-pack hero for years to come. For the sake of contrasting with the other characters and showing what typical U.A. students are supposed to be like, however, Mina is doing a wonderful job. Most importantly, she doesn't mind being mediocre so stars like Izuku and Shoto can shine that much brighter. In a way, that makes Mina more heroic than anyone.
