One Punch Man and My Hero Academia are two of the most popular superhero manga series out there, with massive fights, monsters, and struggles over hero rankings. While these series have some very different takes on what it means to be a hero, it's hard to resist comparing them, especially when it comes to those rankings.
While My Hero Academia's rankings tend to be based on popularity, societal impact, and number of cases involved, One Punch Man's Hero Association rates its heroes based primarily on power level, with popularity having some impact at the higher levels. An S-class hero in One Punch Man should be capable of taking on the toughest threats imaginable, while a C-class hero is mostly stopping purse thieves and other low-level crimes. But if this same sort of threat analysis were conducted on some of the pro heroes in My Hero Academia, how would they stack up?
Shota Aizawa (Eraserhead)
The homeroom teacher for hero class 1-A, Shota Aizawa, AKA Eraserhead, is a pro hero with the ability to erase a person's quirk (superpower) for as long as he looks at them. His eyes are often bloodshot from trying to keep them open as a result, since he's very aware of the limits of his quirk. It's well-suited for teaching students, since Aizawa can use his ability to keep them from hurting themselves or losing control, but it doesn't work against those with mutant-type quirks—the ones that change a person's physical appearance permanently.
As a result of this limitation, it seems unlikely that Aizawa's quirk would be effective against many of the monsters and other threats that show up in One Punch Man, especially considering it hasn't been effective on the Nomu. Aizawa's other main weapon is his nearly indestructible scarf, which he calls his Capturing Weapon. He often uses this to restrain and impede his opponents, and he's very skilled at using it. Still, sufficiently powerful enemies are capable of escaping it, especially if his quirk isn't effective against them.
With these factors taken into account, it seems likely that Aizawa would be an A-class hero, although likely on the lower end. Aizawa could probably defeat Fubuki, the top B-class hero, but he might struggle against some of the higher members of A-class.
Nemura Kayama (Midnight)
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The R-rated hero Midnight is also a member of the faculty at UA High School. Her quirk allows her to put people to sleep, making them highly suggestible, by emitting chemicals from her skin. Since her ability functions better with a greater area of skin exposed, she often wears risqué outfits, and was singlehandedly responsible for causing the regulation of superhero costumes. While her ability does work on both men and women, it's more effective on men, although it's implied that attraction to her is a factor.
Midnight has some martial skills, mostly relating to her use of whips. Like Aizawa, her quirk isn't the most combat-oriented, so she likely wouldn't fair well against powerful monsters, especially feminine ones like DO-S, who has comparable themes and powers. On the other hand, most monsters seem to be masculine, and several were once human, so her quirk may be more effective on them than expected.
A solid B-class rating for Midnight seems most likely; while she's a respected hero in My Hero Academia's world, which accommodates for the utility of a hero's quirk in disaster and search and rescue scenarios more, her capacity to take down major threats just isn't great enough to place her much higher.
Toshinori Yagi (All Might)
The former #1 hero and the most famous pro in My Hero Academia, All Might became the "Symbol of Peace" for a reason—he's just that strong. All Might's commitment to being a hero runs deep, and he has a dedication to heroic values like service and self-sacrifice. While All Might certainly tends to a take a beating more often than Saitama, his spirit provides him with the inner strength to continue onward, regardless of the circumstances.
One for All, his quirk, provides him with an incredible level of super-strength, such that his punches can disturb weather patterns for miles around. In One Punch Man, the only character that's shown an ability like that is Saitama himself, so there's no doubt that All Might is up there in the rankings, even in another world. But since Saitama's ranking isn't the most accurate, he isn't a good gauge for All Might. He's quite fast as well, and One for All also provides him with enhanced durability and stamina, meaning All Might can hang in a fight for a very long time. Often, his greatest weakness is the sheer amount of collateral damage that can take place when he lets loose—yet another parallel with Saitama.
All Might is probably the easiest My Hero Academia pro to rank, simply because he's clearly at the top. He firmly belongs in S-class, and is very likely near the top, especially when at his peak.
Enji Todoroki (Endeavor)
The current #1 hero and former #2 behind All Might, Endeavor is the Flame Hero, wielding incredible fire-based powers that make him a major force when it comes to fighting evil. While Endeavor has some questionable ethics and seems to be much more concerned with his ranking for personal reasons than because he wants to do good, he does still put his life on the line to fight villains. He's been the #2 hero for over 25 years, giving him a wealth of experience and skill to draw from.
While his abilities never quite match up to All Might's, he also has exceptional stamina and durability, and his physical strength seems to far exceed a normal human's capacity. He can create and control flames, which he uses to enhance the power of his attacks further, although overheating is a major weakness as a result. These powers are probably most comparable to the A-Class, rank 6 hero Blue Flame in One Punch Man, although Endeavor's abilities seem to exceed Blue Flame's. Endeavor's unwillingness to cooperate and team up with other heroes is pretty typical of high ranking heroes in the Hero Association, so he'd likely fit in well in their structure.
Endeavor is very likely an S-class hero as well. While All Might is probably on the higher end, Endeavour might be closer to the middle. Heroes like Tatsumaki and Silver Fang would still be able to deal with him, but lower-ranked S-class like Puri Puri Prisoner could easily be defeated by Endeavor.
Keigo Takami (Hawks)
Hawks, the Wing Hero, is currently the #2 hero behind Endeavor, and was #3 before. At just 23 years old, Hawks is much younger than most heroes on the top ten list in My Hero Academia. His quirk is that he has red, angel-like wings on his back, and is capable of controlling each and every feather individually. These feathers can grow back if destroyed, and return to their place when detached. The feathers on their own or in small groups are often capable of lifting entire adult humans, making them akin to a fleet of drones when in a major disaster scenario. He can also use the largest feathers as sword-like blades, and his wings are strong enough to carry others with him, if need be. He even has an ability similar to Spider-Man's spider sense, warning him of coming danger.
While Hawks appears fairly late in My Hero Academia's story compared to most of the above, who've been present since the beginning, his powers are certainly not something to take lightly. He's very fast and well-trained, but he doesn't have the phenomenal physical strength of his top-ranked colleagues. His feathers don't seem to have a maximum range, or if they do, he hasn't been shown reaching it yet. This gives him an amazing range of attack, as well as the ability to effectively operate in many locations at once. While there aren't any direct parallels in One Punch Man's Hero Association, it's clear that with this kind of power at his disposal, he could deal with most of the monsters they've faced without issue.
Hawks is another solid S-class hero, and arguably might even surpass Endeavor to enter the upper echelon of S-class, alongside Blast and Tatsumaki, if only due to the versatility of his quirk.