Their relationships would likely develop in a very positive way. Ace already has a connection with Whitebeard. When Sabo and Luffy join, they would be welcomed into the family - like atmosphere of Whitebeard's crew. Luffy, with his infectious enthusiasm, would quickly make friends with the other crew members. Sabo, being more serious - minded, would earn respect for his skills. Ace would act as a sort of bridge between them and the rest of the crew, and over time, they would all become closer, sharing their dreams and fighting side by side.
Ace's relationship with Whitebeard is already established, but it could grow to be more of a father - son type relationship. Luffy would be in awe of Whitebeard and his crew, and his relationships with everyone would be based on his infectious enthusiasm. Sabo, being the more rational one, would study Whitebeard's leadership style and learn from it. As for the relationship between the three brothers, they would support each other during battles and share their dreams and experiences with the rest of the crew, which would in turn strengthen their bonds with the Whitebeard pirates.
In fanfiction, their relationships are sometimes explored through shared battles. For instance, they might all fight together against a common enemy, like a powerful navy fleet. During these battles, the trust between Ace, Sabo, Luffy, and the members of Whitebeard's crew is emphasized. The relationships are also shown through quieter moments, like when they are all on the ship sharing stories and dreams, which helps to strengthen the bond between them all.
Well, perhaps the fanfic could be about how Ace, Sabo, and Luffy's different personalities interact with the Whitebeard pirates. Luffy's carefree nature might bring some chaos and fun to the crew. Ace's loyalty and strength could earn him a special place, and Sabo's intelligence could be used to solve some tricky situations that the crew gets into while sailing under Whitebeard.
Well, in fanfiction, Luffy's bond with Ace and Sabo is unbreakable. They grew up together and share a lot of memories. When it comes to the Marines, they represent the 'order' that Luffy and his brothers are sort of defying as pirates. Some fanfictions might show a young Marine recruit who has a change of heart after seeing the strong bond between Luffy, Ace, and Sabo. He starts to question whether the Marines are always in the right. Usually, though, the Marines are there to create conflict for the trio.
Well, perhaps in the fanfic, there could be a plot where Whitebeard decides to train Ace, Sabo, and Luffy in a new form of combat. This training could lead to them developing new powers or techniques. Also, they might get involved in a political intrigue within the pirate world while associated with Whitebeard. Like, they have to deal with other pirate lords who are jealous of Whitebeard's influence and try to undermine him by targeting the three brothers.
In this 'ace sabo and luffy swap bodies fanfic', they would first likely be extremely confused when they wake up in each other's bodies. Sabo might be the one to figure out what's going on first and try to help them adjust. Luffy in Ace's body could end up accidentally using Ace's powers in a more reckless way than Ace would. And Ace in Luffy's body might have a hard time getting along with Luffy's crew at first because he's so used to his own group.
A plot could revolve around a tournament on an island. Ace, Sabo, Luffy, and members of Whitebeard's crew participate. The prize is a powerful devil fruit. Each character has their own reasons for wanting it. As the tournament progresses, old rivalries are rekindled, new friendships are formed, and they all discover more about themselves and their place in the pirate world.
One common theme is brotherhood. Since they are like brothers in the original story, fanfics often explore and strengthen this bond. Another theme is adventure. They are all adventurous characters, so fanfics usually involve them going on exciting quests.
Probably Luffy. He's not really the most perceptive when it comes to complex situations like body - swapping. He might just wake up and start doing his normal things without realizing he's in Ace's body at first.
Luffy's character would likely become more mature. He'd learn discipline from Whitebeard's strict training regime. His view of the pirate world might expand as he gets insights from Whitebeard's long - standing experience.