Humor is also a big theme. Since Saitama is such a non -chalant and often deadpan character, his interactions with characters from other universes tend to be really funny. In a crossover with Pokémon, for instance, his reaction to the cute but sometimes powerful Pokémon is both humorous and unexpected.
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.
One common theme is the exploration of Saitama's power in different universes. For example, when he crosses over to a universe with magic, how his physical strength compares to magical abilities.
A fanfiction might center around a competition between Popeye and Saitama. They could have a friendly contest to see who can defeat the most villains in a day. Popeye would use his wits and spinach - enhanced strength, while Saitama would rely on his incredible punching power. This could lead to some hilarious and exciting encounters as they both try to outdo each other.
A crossover with 'Dragon Ball' would be cool. Picture Saitama facing off against Goku. It would be an interesting contrast between Goku's love for a good fight and Saitama's boredom with opponents who can't challenge him.
One possible plot could be that Saitama somehow ends up in the Marvel universe. He might be mistaken for a new superpowered being by the Avengers. Maybe he just casually punches a big bad like Thanos during one of his attacks, completely oblivious to the whole situation, leaving the Avengers both shocked and amused.
How about a crossover with 'Attack on Titan'? Saitama could find himself in the world of the Titans. His ability to defeat any enemy with one punch would be extremely useful against the Titans. He might not understand the complex politics and fear that surrounds the people in that world at first. But as he starts taking down Titans left and right, he would become a sort of legend among the survivors.
The plot could involve Garou somehow ending up in Saitama's world more permanently. Maybe he decides to team up with Saitama against a common enemy. This new enemy could be a powerful being from another dimension that neither of them could face alone. Their contrasting fighting styles would make for an interesting dynamic, with Saitama's one - punch power and Garou's martial arts skills.
It's hard to say. Saitama has the ability to defeat any enemy with one punch, but Goku has an array of powerful forms and techniques. However, Saitama's strength seems to have no limit that we've seen so far. So, in a straight - up fight, Saitama might have the edge just because of his one - punch ability.
The plot could involve Saitama from One Punch Man being transported to the world of Overlord. He might initially be confused by the different magic - based setting. Since Saitama is so overpowered, he could end up accidentally causing chaos in the new world. For example, he might punch an enemy so hard that it creates a massive crater, which the inhabitants of the Overlord world have never seen before.