Well, in these fanfics, there could be a scenario where Saitama and Naruto team up to fight a common enemy. Maybe an alien invasion that threatens both the One Punch Man world and the Naruto world. They would bring their own unique skills to the table. Saitama with his incredible strength and Naruto with his vast array of ninjutsu. Also, imagine if Naruto tries to learn Saitama's secret to his strength, thinking it's some kind of super - ninjutsu.
In some One Punch Man x Naruto fanfics, there might be a crossover of the settings. For example, Konoha village could be visited by Saitama. The villagers' reactions would be quite funny, seeing a bald man with such extraordinary strength. And on the other hand, Saitama might be introduced to ramen in Konoha, which he would probably love. Naruto could also show Saitama some of his most powerful jutsus, like the Six Paths Sage Mode, and Saitama would be his usual nonchalant self, but still impressed deep down.
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.
I'm quite sure there exists a 'Naruto is One Punch Man' fanfic. The world of fanfiction is vast and full of all kinds of creative crossovers. Writers might be intrigued by the idea of bringing Naruto's ninja skills and the unique world of One Punch Man together. For example, how would Naruto react to the overpowered villains in One Punch Man's world? And how would Saitama view Naruto's determination to protect his village? These are the kind of things that could be explored in such a fanfic.
One common theme is power comparison. Since both Naruto and One Punch Man have characters with extraordinary abilities, fanfics often explore how Naruto's chakra - based powers stack up against Saitama's strength. Another theme is the clash of cultures. Naruto's ninja world has its own set of values and rules, which is different from the modern - day - ish world of One Punch Man.
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.
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 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 idea could be that Naruto and Saitama somehow end up in a shared dimension where they have to team up to defeat a common enemy. For example, a powerful demon from Naruto's world that has the ability to regenerate like some of the monsters in One Punch Man's world. Another plot could involve Naruto learning Saitama's training regime and trying to incorporate it into his own ninja training, while Saitama is intrigued by Naruto's chakra system and tries to figure out if he can use it to make his punches even more powerful.
One interesting crossover could be Naruto learning some of the X - Men's powers. For example, he might gain the ability to control magnetism like Magneto and use it in combination with his own chakra control for unique attacks.
There's 'The Meeting of Heroes: Naruto and Saitama'. This fanfic focuses on a scenario where Naruto and Saitama meet. It plays around with their different personalities. Naruto's determination and Saitama's nonchalant attitude create a great contrast that makes for an engaging read.
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.