Warning: spoilers ahead for Ayashimon chapter 1!
The hero Maruo in Shonen Jump's newest manga Ayashimon faces the same existential crisis as Saitama in One Punch Man. Both characters have subjected themselves to a ridiculous amount of training to achieve a similar goal and suffer as a result because of the insane amount of power they now wield.
Ayashimon by mangaka Yuji Kaku (Hell’s Paradise) makes it abundantly clear in the debut chapter what Maruo wants more than anything else: to become a hero like his favorite manga protagonists and experience the same epic battles as they do against insanely powerful villains. While an absurd dream, what he accomplishes to get there is even more ridiculous. He tries the very same things as his favorite manga heroes to amass power, for example training by punching rocks (and therefore breaking his hand.) Surprisingly, however, he does achieve the seemingly impossible. He can now smash rocks like manga heroes - and so much more. He is so incredibly powerful that every fight he's ever gotten into is a cinch - and like Saitama, he hates it.
Maruo wanted to experience an epic battle like his favorite manga heroes - and that entails struggling and getting beat up. Victory is now coming too easily. Depressed, Maruo begins hunting for a job because, naturally, getting into so many fights has resulted in his expulsion from school. But because of his brute strength, he only succeeds in destroying everything he touches. Even dojos won't accept him. This is exactly the same challenge that Saitama contends with in One Punch Man. Saitama famously obtained his unmatchable strength from undergoing a simple regimen of 100 push-ups, 100 sit-ups, 100 squats, and 10 kilometers of running each day for over a year. As a result, he can somehow defeat any enemy with one punch. And like Maruo, Saitama is not pleased with this turn of events, reaching a point where he desperately wants to fight an enemy who will test him. So far, this goal eludes him, leading to constant misery.
While inherently similar, Maruo does something that Saitama would never attempt, all for the hope of experiencing a real fight like his manga heroes. Maruo falls into the service of Urara, the boss of a Yakuza gang that consists of Ayashimon, or monsters. This is akin to Saitama joining the Monster Association so he can fight against Blast, the S-Class Rank 1 professional hero of the Hero Association. Of course, Maruo initially denies Urara's request to join her because it's something his manga heroes would never do. They are protagonists after all, not antagonists. But after he fights against a rival Ayashimon Yakuza gang that attacks Urara, he becomes so excited about how badly they've beaten him up and how much effort he had to put into the ensuing battle that he throws aside his ideals and swears fealty to her through a blood pact.
Ayashimon is undoubtedly a blatant rip-off of One Punch Man in regards to how much Maruo and Saitama struggle with being too powerful. The new Shonen Jump series even borrows a similarly satirical tone as the more established manga but rather than poking fun at superpowered fights and the horrible banter between heroes and villains, Ayashimon hones in on Maruo's obsession with manga heroes to the extreme where he even creates his own version of Goku's Kamehameha wave. There are even grotesque monster villains in each series, but the main divergence is Maruo's willingness to join a villainous organization to experience what he craves. Hopefully Ayashimon will capitalize on this difference in future issues of Shonen Jump, as one way it can set itself apart from One Punch Man will be to follow its hero's corruption rather than their rise to fame.