Kim GiGyu from the new manga The Player That Can't Level Up is the exact opposite of Saitama from One-Punch Man. The latter stars a superhero who amassed such amazing power through an assorted arrangement of highly extensive and demanding training regimens that he can literally defeat anyone by punching them once. While the other, well, can't level up - at all. Kim is perpetually stuck at level one no matter how many goblins he slaughters, despite having been blessed with the coveted unique retainer skill. However, both series have much more in common through their respective differences besides their protagonists being complete opposites and just happening to share highly revealing titles that essentially explain their entire plots almost too much.
The Player That Can't Level Up's entire story is predicated on one moment 18 years ago when a tower suddenly appeared on Earth and unleashed a horde of monsters onto the unsuspecting public. Luckily, a small minority of humans were serendipitously blessed with powers at the exact same moment as the monsters' unwelcome arrival. Fighting off this horde's relentless assaults has culminated in these so-called players being understandably showered with wealth and untold glory. But Kim GiGyu? He's just a regular guy. At first.
His life changes when Kim is suddenly asked to become a player - when even more surprisingly, he learns he's a unique ability retainer: a player whose powers manifest much later than most, but when they do, usually transform them into gods. The irony is that Kim can't level up regardless of his incredibly lucky circumstance. Although this unfortunate development makes him the complete opposite of Saitama, Kim being incredibly weak and One-Punch Man's Saitama possessing unmeasured strength isn't the only example of how both series are completely different. Their unique divergences are also extremely ironic.
One would expect that Saitama would be beloved by all and regarded as the most insanely strong hero of all time. But he's not. That's because no one knows about him and his true power, except a select few. Saitama doesn't seek fame nor recognition. All he wants is to find an opponent who he can't defeat simply by punching them once. He yearns for a challenge. For that reason, he rarely ventures out to defeat monsters when they attack since he knows they're not worth his time, robbing the world from witnessing his sick skills in action. This strange phenomenon happens more often later on in the series after Saitama becomes utterly obsessed with fighting video games, most likely because he's not very good ... at all. And when he joins the Hero Association, he's given a weak ranking instead of being labeled as an S-Class hero because no one knows of his true strength. But, again, he doesn't object to this nor does he even attempt to rectify this travesty since he doesn't care.
Meanwhile, no one should know who Kim is in The Player That Can't Level Up because he's insanely weak. But because he's a unique skill retainer, people naturally know about him already. Add that to the fact he's a unique skill retainer who's somehow weaker than every other player, and he becomes a bonafide enigma, a pathetic enigma, at that. Word will get around fast when a player who's supposed to be one of the most powerful and beloved warriors of all time is actually weaker than everyone else.
Because of Kim's unique situation, it's understandable why The Player That Can't Level Up written by 앵무새 with art by 박정재 and 스튜디오 크힛 is already quite popular, despite there being only 20 or so chapters translated into English by fans. Readers know that Kim should be strong and want him to be strong, but he's not. Similarly, One-Punch Man fans know Saitama's the strongest hero out of the many other characters in that universe, and yet he doesn't receive the recognition he overwhelmingly deserves. And it's maddening.