Well, it could be about Naruto having some sort of dark powers inherited from the 'devil' figure. Maybe he has to struggle with these powers and how they are perceived in the ninja world. He might face a lot of prejudice from his friends and the village at first.
It could be the traditional enemies of Naruto like Orochimaru. Since Naruto has this new 'son of the devil' aspect, Orochimaru might be more interested in him to use his powers for his own evil purposes.
In such a fanfiction, perhaps Naruto could be shunned by the village from the start. His 'devil' heritage might give him strange powers that he has to hide. He could struggle with self - identity, different from the Naruto in the original who is seen as a hero. Maybe he has to fight against the prejudice of the people who believe the devil's son can only bring destruction.
The village elders could be antagonists. They might see Naruto as a threat due to his devil - like origin and try to eliminate him. They fear that his powers could bring chaos to the village.
He might become more confident, bordering on over - confident like Gilgamesh. Naruto is already confident, but with Gilgamesh as his father, he could have an even greater sense of self - importance.
In most One Piece lore, those who eat Devil Fruits lose the ability to swim. However, in this fanfiction, perhaps the author has created a unique workaround. Maybe Naruto has some special jutsu or power-up that allows him to overcome the typical Devil Fruit drawback and swim. Another possibility is that the Devil Fruit he has is an entirely new type, not bound by the normal rules, which gives him the ability to swim.
The devil could be a new, mysterious character created specifically for the fanfiction. It might be an ancient evil entity that has been lurking in the shadows of the Naruto world for ages.
Yes, there are likely some fanfictions out there with such themes. You can try searching on popular fanfiction websites like FanFiction.net or Archive of Our Own. Just type in 'godlike naruto devil' in the search bar and see what comes up.
If Naruto gets a devil fruit in fanfiction, his character development would be quite interesting. He has always been known for his hard work and determination in mastering chakra - based techniques. Now, with a devil fruit power, he would have to start from scratch in a way. He'd need to train to fully utilize the devil fruit abilities. This process of learning something completely new would likely make him more humble as he realizes there's always more to learn. It could also make him more creative in combat, as he combines his old skills with the new devil fruit powers.
If Naruto found a devil fruit, it would open up a whole new world of possibilities for his adventures. He could travel to different lands in search of more knowledge about the devil fruit. Maybe he'd encounter other characters from different fictional universes who are also interested in devil fruits. His understanding of power and the world around him would expand. He'd no longer be just a ninja from the Hidden Leaf, but someone with a power that bridges different fictional concepts. This could lead to him becoming a sort of ambassador between the Naruto world and the world of One Piece - like elements introduced by the devil fruit.