One idea could be a male OC who has the power of telekinesis. He could be a former scientist who was exposed to some strange radiation during an experiment. This power would set him apart from the existing characters in One Punch Man. He might initially struggle with controlling his power, leading to some comical or dangerous situations.
You could create an OC who is a gamer in the One Punch Man universe by giving them a special power related to video games. For example, they might be able to use 'power - ups' from games in real - life battles, like a speed boost or invincibility for a short time. Their backstory could be that they were a normal gamer who got sucked into the One Punch Man world and had to adapt their gaming skills to survive.
For a One Punch Man Monster OC in fanfiction, consider its weaknesses. Even though it's a monster, it can't be all - powerful. Maybe it has a fear of bright lights, so heroes could use that against it. Its personality could be really cocky because of its unique powers, but that could also be its downfall. It might underestimate its opponents and get beaten as a result.
One idea could be that Saitama's hair gives him some new, unexpected power. For example, his hair could start to glow and act as a power amplifier, allowing him to defeat enemies even more easily than before. This would be a fun twist on his already overpowered character.
Another fanfiction concept could be that the monsters in the 'Danmachi' dungeon start to mutate in a way similar to how the monsters in 'One Punch Man' are strange and powerful. This would force the adventurers in 'Danmachi' to come up with new strategies, and perhaps some of the heroes from 'One Punch Man' could come to help out, like Genos, who could provide some technological insights on dealing with these new threats.
Here are some plot ideas. The Dragon OC could be a reincarnation of an ancient and powerful dragon. It gradually remembers its past life and powers as it interacts with the characters in One Punch Man. It might start as a weak - looking creature but as it unlocks its memories, it becomes extremely powerful. Another plot could involve the Dragon OC being hunted by a secret organization in the One Punch Man world because of its unique dragon DNA. This organization wants to use its DNA to create super - soldiers, and the Dragon OC has to fight back and expose this evil plan.
To create a Dragon OC in One Punch Man fanfiction, start with appearance. A dragon OC might have scales that change color depending on mood. Then, for the powers, it could have super strength combined with the ability to fly at supersonic speeds. Also, in terms of relationships, it could start as an enemy of Saitama but later become an ally.
One idea could be a crossover where Spider - Man and One - Punch Man team up to fight a common enemy. Maybe a powerful villain from the Spider - Man universe has somehow made its way into the One - Punch Man world and is causing chaos. They could learn from each other's fighting styles. Spider - Man with his acrobatic moves and web - slinging, and One - Punch Man with his overwhelming strength.
A possible plot is that the OC is a former enemy of Fubuki who has seen the error of their ways. They try to make amends by helping Fubuki in her quest to become stronger and more respected in the hero community. This could involve training sessions where the OC shares some unorthodox fighting techniques that complement Fubuki's psychic powers. The OC could also have connections to some powerful and mysterious figures in the One Punch Man universe, which could open up new storylines for Fubuki.
Another idea is that Naruto, curious about other powerful beings, uses a jutsu to travel to the One Punch Man universe. There, he would be amazed by Saitama's strength. Naruto could try to learn from Saitama how to be so effortlessly strong, but Saitama would probably just shrug it off and say there's no special trick. They could team up to fight some of the monsters in Saitama's world, with Naruto using his ninjutsu and Saitama just punching things away.
First, focus on the character's origin. Explain how your male OC got his powers or what led him to become the person he is. For example, if he has super strength, was it a genetic mutation or the result of some training? Then, create a conflict. Maybe he wants to join the Hero Association but faces discrimination because of his unorthodox methods. This conflict will drive the story forward.