A possible plot is that a group of Celestial Dragons decide to hunt Luffy for sport. But Luffy turns the tables on them. He leads them on a wild goose chase across different islands. Along the way, he befriends some of the local animals on each island and uses them to play tricks on the Celestial Dragons. For example, on an island full of monkeys, he teaches the monkeys to steal the Celestial Dragons' hats and run away with them, leaving the Celestial Dragons frustrated and looking rather silly.
One idea could be that Luffy accidentally discovers a secret about a Celestial Dragon that could change the power balance in the One Piece world. He then has to decide whether to expose it or use it to his advantage.
In a Luffy Celestial Dragon Fanfic, the class struggle can be shown through Luffy's interactions with the Celestial Dragons. Luffy, who comes from a humble background, can represent the common people. His disregard for the Celestial Dragons' status and power can be a way to highlight the unfairness of the class system.
One potential character could be an old friend of Luffy's mother from her celestial dragon days. This friend might have different views now and could either help or hinder Luffy depending on their own motives. Another could be a servant who knew about Luffy's mother's secrets and has been waiting for the right time to reveal them to Luffy.
In this fanfic, Luffy might team up with some of the oppressed people against the Celestial Dragons. For example, he could meet a group of slaves who were once owned by the Celestial Dragons. Luffy, being the freedom - loving pirate he is, would vow to free all of them and take on the Celestial Dragons in a big showdown. They could use their wits and Luffy's unique abilities to outsmart the arrogant Celestial Dragons.
Yes, in some fanfictions, Luffy can be more like Dragon. Luffy and Dragon both have a strong sense of justice. Luffy wants to become the Pirate King and free the oppressed islands, which is similar to Dragon's goal of overthrowing the World Government to create a more just world. Also, they both possess great leadership. Luffy leads his crew, and Dragon leads the revolutionary army.
The World Government could be the main antagonist in a more complex way. They could be secretly manipulating events to pit Dragon and Luffy against each other. For example, they could spread false rumors about Luffy being a tool of the revolutionaries, which would make other pirate crews and kingdoms target him, and at the same time make Dragon look bad for having a son who is causing so much chaos. This would force Dragon and Luffy to either fight each other or find a way to clear their names together.
Well, one possible plot could be that Luffy, while on one of his adventures, accidentally stumbles upon Dragon in a secret island. They initially don't recognize each other, but then some events unfold that make them realize their connection. Maybe they end up having to team up to fight against a common enemy that is threatening the freedom of the island's inhabitants.
One idea could be that Luffy somehow gains the power to slay dragons in a special arc. Maybe he encounters a dragon that is terrorizing an island and he has to use his Gum - Gum powers in a new and creative way to defeat it. For example, he could stretch his arms around the dragon's neck and then use his Haki to stun it before delivering a final blow.
A powerful dragon - themed pirate could be the main antagonist. This pirate has a crew of dragon - like creatures and they are causing chaos across the seas. They have a grudge against Luffy for some reason, perhaps because Luffy has unknowingly entered their territory or stolen something valuable from them.