Yes, there might be such a fanfiction out there. The concept of crossing over Naruto into the One Piece world as a Celestial Dragon is quite an interesting and unique idea. Fanfiction writers often come up with all sorts of wild crossovers, and this could be one of them. However, it might not be very common as it combines two very different universes in a rather unexpected way.
There's also 'Dragon - Pirate Alliance'. This fanfiction delves deep into how the Z - Fighters and the Straw Hat Pirates would form an alliance. It explores the different cultures and fighting styles of the two groups. For example, how Vegeta's pride would interact with Zoro's sense of honor, and how Gohan's intelligence could be used in conjunction with Nami's strategic thinking.
The fact that it focuses on the Celestial Dragons. In the One Piece world, they are such a distinct and often hated group. Fanfics about them can explore their opulent lifestyles, their sense of entitlement, and how they contrast with the rest of the world.
A 'Naruto is a Celestial Dragon' One Piece fanfiction could explore how Naruto's presence disrupts the existing power structure among the Celestial Dragons. He could introduce new ideas of equality and strength based on his own experiences in the Naruto world. His relationships with the different races in One Piece, like the Fish - men and the Minks, could also be a major part of the story. He might even try to reform the system of slavery that the Celestial Dragons are often associated with, using his influence and his unwavering belief in justice.
Sabo could be a popular character in One Piece Celestial Dragon fanfic. Given his revolutionary ideas and his past encounters with the Celestial Dragons, he could be a key figure in stories that aim to take on the corrupt system. Also, some of the Straw Hat crew members like Nami, who has a strong sense of justice, might be involved in stories where they oppose the Celestial Dragons' tyranny, making her popular in these fanfics.
One interesting concept could be exploring the backstories of the Celestial Dragons in more depth. Maybe they have some hidden motives or past traumas that led them to become so despised. Another could be the idea of a Celestial Dragon turning against their own kind, which would create a lot of drama and conflict within the One Piece world.
For an OC Celestial Dragon, you could make them a young and naive character at first. They grow up believing all the propaganda about their superiority. But after a chance encounter with a kind - hearted commoner, they start to question everything. They could have unique physical features like silver - white hair and purple eyes, and always wear elaborate, gold - trimmed robes.
One idea could be an OC Celestial Dragon who rebels against the system. They see the cruelty and inequality within the Celestial Dragons and decide to use their position to secretly help those in need. They might start by providing food and shelter to slaves in hiding places they create within their own grand estates.
They blend the universes by incorporating the power systems. For instance, in some fanfictions, characters might use Devil Fruits while also having the ability to sense and use ki. Also, character interactions play a big role. Luffy's carefree nature might influence Goku's more straightforward approach to life.
One possible plot could be that Goku and his friends somehow end up in the One Piece world. They meet Luffy and his crew. Goku might be interested in the Devil Fruits and their powers. Luffy, on the other hand, would be excited to see Goku's super strength and ki abilities. They could team up to fight a common enemy like a powerful pirate who has also acquired some sort of dragon ball - like artifacts. This would lead to an epic adventure with both the Saiyans' and the Straw Hats' unique fighting styles combined.