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.
His fighting style would become more diverse. If he got a devil fruit, say the Ope Ope no Mi (Operation - Operation Fruit), he could create rooms and manipulate objects within those rooms. This would be a huge departure from his normal ninja attacks. He could trap enemies in these rooms and then use his kunai and shuriken skills within the confined space to defeat them.
His fighting style would become more diverse. If it was a Paramecia devil fruit, say the Gomu Gomu no Mi, he could stretch his limbs like Luffy. This would add a whole new dimension to his close - combat skills, allowing him to reach enemies from a distance and perform acrobatic attacks that his normal ninja training might not have included.
If Naruto ate a Zoan devil fruit, say, of a bear, he would probably become more muscular and hairy. His face might change to have a more bear - like snout and his teeth could become larger and sharper. His hands and feet might also transform into bear paws, which would give him better grip and more power in his attacks.
If Harry Potter ate a devil fruit in fanfiction, his identity would be more complex. He would no longer be just a wizard. He would be a wizard with the extraordinary powers of a devil fruit. His battles would be different. He could use his devil fruit power to surprise his enemies. For instance, if he had a devil fruit that allowed him to turn invisible, he could use it in combination with his disillusionment charm for an even more effective stealth approach. His life would be filled with new adventures as he explored the limits of his combined powers and tried to keep them a secret from those who might misuse this knowledge.
The ninja world could change a great deal. If Naruto abandons a devil fruit, and it falls into the wrong hands, like say Orochimaru's, he could use it to create even more powerful and terrifying jutsu. This would force the other ninja villages to band together against this new threat. Also, the concept of power in the Naruto world would be redefined as devil fruit powers are so different from chakra - based abilities.
If Naruto got the ice devil fruit in fanfiction, it would change the balance of power in the ninja world. His village, Konoha, would become a more formidable force as he could use the ice to defend it more effectively. Enemies approaching the village might find themselves trapped in ice barriers. Also, his training would change. He'd have to train with different types of opponents who can deal with ice attacks, like those from the Snow Country. His new power could also attract new enemies who are interested in the ice devil fruit's power.
Naruto's story in this fanfiction would see him evolving in a different way. With the Phoenix Devil Fruit, he might not rely as much on his chakra training. Instead, he'd focus on mastering the powers of the fruit. This could lead to a split in the way the ninja world views him. Some might see him as a freak with strange powers, while others would see him as a new kind of hero. His journey to become Hokage might also change as he has to prove that he can use these new powers responsibly.
Naruto's personality might become more confident. Having the power of a Logia devil fruit would make him feel even more capable in battles. He might be a bit more reckless too, as he tests out his new powers.
In Naruto fanfiction, a godlike Devil Fruit would be a game - changer. Imagine a Devil Fruit that gives the user the power to read minds. This would be extremely useful in espionage and combat. In the Naruto world, where information is crucial, this power could turn the tides of war. However, it might also have negative consequences. The character with this power could become corrupted by the knowledge they gain, or other characters might fear and isolate them due to the invasion of privacy.
His character would become more powerful. The devil fruit power would add a new dimension to him.