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.
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.
One character that would make for an interesting pairing with Doflamingo in a crossover fanfiction is Zoro. Zoro's strong sense of justice and his skills as a swordsman would clash with Doflamingo's devious ways. They could have epic sword battles, and Zoro might be the one to cut through Doflamingo's strings, both literally and metaphorically. Also, Nami could be paired with Doflamingo. Nami's intelligence and ability to manipulate situations for her own gain, although in a more positive way compared to Doflamingo, could lead to some really interesting interactions. She could try to outwit him in a game of wits.
One idea could be that your pet Doflamingo has a unique ability that helps the Straw Hat crew in a strange way. For example, it can sense danger from far away, like when the crew is about to be attacked by the Marines. It might use its flamboyant appearance to distract the enemies while the crew escapes.
Sure, it's highly likely that there are fanfics like this out there. In the world of 'One Piece' fanfiction, all kinds of scenarios are explored. A story with female Luffy and Doflamingo could delve into how their personalities, which are so different in the original series, interact in a new and unique way. It might also play with the themes of good and evil, freedom and control in a different light, depending on how the author writes it.
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.