Well, one possible future for them in Marine fanfiction could be that they form a special unit. Ace with his fire power, Luffy with his rubber abilities and Sabo with his skills would be a formidable team. They could be sent on special missions to deal with the toughest pirates. This way, they are still following their dreams of adventure while being part of the Marines.
Perhaps in this fanfiction, Ace, Luffy and Sabo will make Marineford a place where pirates and marines can live in harmony. They could set up some rules that both sides can abide by.
The idea of Ace, Luffy, and Sabo in the Marines is quite interesting. They could use their bonds to make the Marines a more family - like organization. Their unique abilities would also give them an edge. For instance, Luffy's stretching powers could be used in creative ways during rescue missions or combat.
In this fanfiction, Ace, Luffy and Sabo could have a future in Marineford that is full of hope. Maybe they work together to change the perception of pirates in that place. Ace could use his fire power to protect the weak, Luffy with his unwavering will continues to inspire others, and Sabo with his intelligence devises plans to make Marineford a more inclusive place for both pirates and marines.
One possible plot could be that in the future, Luffy, still driven by his dream of becoming the Pirate King, decides to return to Marinford. Ace and Sabo, who are also with him, have their own reasons for going back. Maybe they want to set things right after the chaos that occurred there before. Luffy could be aiming to make a statement that the new generation of pirates is different and stronger. They might face old enemies or find some sort of hidden treasure or knowledge that was left behind during the previous battles.
His dream of becoming Pirate King might take on a different meaning. Instead of being about freedom and adventure, it could be more about domination. Under Doflamingo's influence, Luffy might see the Pirate King title as a way to rule over others rather than a symbol of the freest person on the sea.
In the fanfiction, their relationships can be delved into through flashbacks. Remembering their time together before the events at Marinford, like their childhood days. As they return to Marinford in the future, they might have different reactions based on their relationships. Luffy might be more impulsive due to his emotional connection with the place where Ace died. Sabo, being more level - headed, tries to keep Luffy in check while also sharing his own feelings. They can have deep conversations about their future plans and how their relationships will support or change those plans.
The theme of acceptance is quite common. Fem Luffy often has to be accepted by the other characters in the story. This could be because she's different due to her gender or her slightly different personality traits. Also, the theme of self - discovery is prevalent. As fem Luffy navigates the pirate world, she discovers more about herself, her abilities, and her place in the grand scheme of things.
Here are a few recommendations for novels about transmigrating into Luffy:
1. [One Piece: Shadow Assassin]: This novel tells the story of an assassin's adventures in the world of pirates.
2. [One Piece: The Imitation Master on the Hat Boat: The protagonist of this novel has obtained the special ability to imitate others and tells his story in the world of One Piece.]
3. One Piece: Dominate the World: The male protagonist traveled to the world 16 years after Luffy became One Piece. Together with Luffy, he eradicated despair and demonstrated the operation and power of the world of pirates.
I hope these recommendations will meet your needs.
Nami could also be a common character. She might help Luffy manage the financial aspects of his admiral duties, as well as use her navigation skills to assist in any navy - related voyages. And of course, she'd be there to keep Luffy in check when he gets too carried away.