There's Batman. There's Superman. There's Wonder Woman. There's I-have-every-paranormal-ability-in-the-universe-man (or woman).
Then there's Saitama.
That's the question most people ask when a shockingly normal superhero who started off bashing monsters for fun (and for free) bursts out of his apartment in Z City and onto the pro hero scene in what looks like a borrowed Shazam costume. He hasn't even made it to the most elite class of heroes yet.
So why is he the next best thing in a cape?
It's not because he can vaporize just about anything with one punch. The bald guy otherwise known as One-Punch Man sees himself as anything but the ultimate defender of humanity in spandex. He's obsessed with comics. He fights over losing video games. He snatches up every discount he can find. The thing is, Saitama doesn't go around swearing he's relatable to the rest of us mortals. He just is.
For anyone who thinks you can't be superpowered unless you were born on another planet like Clark Kent or bitten by a radioactive spider like Peter Parker, this is why Saitama is your hero.
He has the same issues as the rest of us...
You normally don't see a hotshot superhero waking up screaming from a nightmare about someone asking him to play rock-paper-scissors with a booger on their finger. Even when other superheroes do have nightmares, they're typically world-ending premonitions and not just about snot.
So what other issues does Saitama have? Beating video games. Finishing an entire comic series. Figuring out what's for dinner and whether he's going to be able to dash to the supermarket on time, because being able to demolish creeps with one punch doesn't mean you can necessarily run at warp speed. Oh, and it really burns him if anyone puts his very obvious baldness on blast.
...and also looks like the rest of us
You couldn't tell Saitama apart from anyone else when he's out of that Shazam suit. Some of his fellow heroes won't go out unless they have their fancy spandex on, but when Saitama is off duty he goes out in jeans and T-shirts and sneakers that make him disappear among the masses. When he isn't wearing his favorite NSFW shirt that he loved so much he had to have it in hoodie form, he might be wearing a button-down with the Japanese character for 'hair' all over it. This is really a thing.
You couldn't tell the casual Saitama apart in a supermarket (the only place he seems to leave his apartment for when he's not on hero duty), except if something with nine heads and eighteen legs showed up and he destroyed the place getting rid of it.
Sure, we've seen a few self-made heroes, but nothing on the scale of Saitama. After a run-in with a monster crab, this guy worked himself within one inch of his life for three years on end, enduring a punishing regimen of 100 sit-ups, push-ups and squats and a 10K run every single day. He's so hardcore that, during that masochistic training phase, he refused to turn off the air conditioning in the deliriously hot and humid Japanese summer. Though he reached a new level of toughness (and dehydration, he also lost all his hair.
At least he got something awesome in return: the ability to take down Godzilla wannabes with one punch.
He cares more about what's for dinner than what could eat him alive
Most superheroes don't suddenly realize they missed the super sale on steak that the supermarket had going on today in the middle of fighting a vicious genetically engineered beast. Saitama is not most superheroes. After he and cyborg sidekick Genos pass the hero exam and listen to the same lecture all new heroes get, dinner is the only thing on Saitama's mind. Do most superheroes even go grocery shopping?
When Saitama is just casually walking back from the supermarket one night, he realizes he forgot to grab seaweed. No problem when a monster with edible seaweed tentacles slithers right in front of him. It's fresh and it's free.
He's easily frustrated…
How many heroes have you seen walk away from some unspeakably horrid creature they just beat, thinking "great, wish I could face a bigger challenge"? That would be a death wish even for the most super of superheroes. Then you have Saitama, who can get rid of things the size of a skyscraper with one punch and wishes it took more effort. He's not relieved for himself or humanity. He wants something harder to beat.
Saitama is such a perfectionistic masochist that what thrills him the most is the rare monster that won't go down with one lethal punch. Nothing is ever too huge for him, but some, like extraterrestrial Lord Boros, have their own arsenal of tricky moves. These are the types of creatures he breaks out his "seriously serious series" of punches for (just watch the video above). As if that wasn't enough, Saitama wishes he could do it more often.
…but he could care less about what other people think
Who saves a city naked and isn’t the least bit self-conscious? Right… the guy who says "oh" in the face of monsters. It's not that Saitama just waltzes into the street naked whenever he feels like it, but when you punch something out and create a massive explosion, that might just turn your clothes to dust. It's just that he seems completely unbothered in his birthday suit. When he's focused on throwing his fist at the enemy, he evidently has no issues about mooning everyone around him.
By the way, there is another hero in this universe who saves the day naked. Puri Puri Prisoner's clothes tear off when he flexes pre-attack, but he's both totally aware he's naked and also convinced that the light of the gods radiates from his bare body.
He's so indifferent it blows your mind
Seriously — who rockets through Earth's atmosphere, lands on the moon, tosses a moon rock around for a couple seconds, and then jumps back down to Earth to knock out the aliens he was fighting a minute ago? Saitama is almost unnaturally chill as he takes in all the catastrophic phenomena going on around him. There's no booming call for all citizens to get out of there as fast as humanly possible. No bombastic declaration he'll save everyone. Just "oh." Gargantuan fish-thing rising from the watery depths? "Oh." Enormous spaceship touching down? "Oh." Potential apocalypse in 20 seconds? Sure.
You can't get Saitama to freak out when it comes to villains and monsters and paranormal experiences. Missing a sale? That, yes. He always freaks out about that.