A great fanfiction concept could involve the Soul Society from Bleach being curious about Saitama's power. They send some of their best Shinigami, like Byakuya or Rukia, to investigate. Saitama, being his nonchalant self, just treats them like normal visitors. This could lead to a series of events where the Shinigami try to understand his power level, which they can't even fathom, and Saitama is just bored by the whole situation.
One interesting crossover could be Saitama from One Punch Man meeting Ichigo from Bleach. Saitama's overpowering strength would contrast with Ichigo's growth - based power. Maybe Saitama could accidentally disrupt a Hollow attack that Ichigo was about to face, leading to some comical misunderstandings as Ichigo tries to figure out who this bald - headed, super - strong guy is.
One interesting crossover could be Saitama from One Punch Man meeting Ichigo from Bleach. Imagine Saitama's nonchalant attitude in the face of Bleach's complex spiritual world. He might just punch away Hollows without breaking a sweat, while Ichigo would be both amazed and a bit frustrated at Saitama's overpowered nature.
One Punch Man's heroes in the Marvel universe could also be a cool concept. For instance, Mumen Rider's sense of justice in a world full of super - powered beings like in Marvel. His simple yet strong - willed nature could inspire some of the street - level heroes in Marvel. And then there's Tatsumaki, her psychic powers could put her in some interesting situations with the likes of Doctor Strange, as they both deal with powerful and otherworldly forces.
Well, a great crossover idea is having the villains from One Punch Man enter the Naruto universe. For instance, Boros arriving in Konoha. The ninjas would be in for a huge shock as they've never faced an enemy as powerful as him. And Naruto would have to think of some really creative ways to defeat him. Also, the idea of Tsunade trying to figure out how to heal Saitama if he ever got 'injured' (which is highly unlikely) could be a humorous and interesting plot point in a fanfiction.
Another idea is a family - like bond forming between the characters. The Parr family could take Saitama in as an honorary member. Dash would be constantly trying to race Saitama, while Violet would be a bit shy around him. And Jack - Jack could be really curious about Saitama's bald head.
One interesting crossover could be the Powerpuff Girls teaming up with Saitama to fight a common enemy. Maybe a super - powerful villain from the Powerpuff Girls' world that is too tough for them alone, but with Saitama's one - punch ability, they can easily defeat it. Another could be the Powerpuff Girls learning Saitama's training regime and becoming even more powerful.
Another aspect of a crossover fanfiction could be the villains. The powerful villains from Fire Emblem, like Grima, might face off against Saitama. Grima with all its dark magic and power would still be no match for Saitama's one - punch ability. This would create a really interesting dynamic as the Fire Emblem characters would have to deal with the fact that their most feared enemy was so easily defeated by an outsider.
Well, a really interesting crossover is when the power systems of both universes collide. For example, when Fairy Tail mages try to understand Saitama's power which is seemingly limitless. It creates a lot of mystery and awe.
One possible scenario in Batman and One Punch Man fanfiction could be a battle of wits between Batman and Saitama. Batman, with his strategic mind, would be intrigued by Saitama's overwhelming strength. Saitama, on the other hand, might be confused by Batman's complex gadgets and plans.
Yes, there could be crossovers where RWBY characters are inserted into the One Punch Man universe. For example, Ruby's speed could be compared to Saitama's in some action - filled scenes. RWBY might enjoy seeing how their powers interact with the crazy power levels in One Punch Man.
A really interesting crossover concept is when the power systems merge. For instance, in a fanfiction, what if Naruto's chakra could be combined with the Sacred Gears in Highschool DxD? And Saitama's power could be something that disrupts or enhances these new combinations. You could have a story where the main character is a hybrid of a Naruto character and a Highschool DxD character, and they seek out Saitama to understand the true nature of power. This would involve a lot of exploration of how the different powers interact, like how Naruto's shadow clones could be used in a battle against Highschool DxD's devils, and how the devils' powers might affect Naruto's jutsu.