In a fanfiction, Ace's own experiences and battles could be related to Luffy's metabolism. Maybe Ace has some knowledge about a special fruit or power that could enhance Luffy's metabolism. He could share this with Luffy, leading to a new adventure where Luffy tries to obtain this thing to boost his metabolism. Also, Ace's death could have an impact on Luffy's metabolism. Luffy could go into a state of shock or extreme grief that either slows down or speeds up his metabolism in an unexpected way.
Well, 'Luffy and Ace: Unbreakable Ties' is a fanfiction that I really like. It focuses on their childhood memories and how those shaped their relationship as they grew up. There's also 'Ace and Luffy's Great Escape' which is full of action. It shows their cleverness in getting out of difficult situations. 'Luffy and Ace: The True Friendship' is a must - read too. It simply and effectively shows the depth of their friendship.
In some fanfictions, Ace's death becomes a turning point for Luffy's character development. It makes Luffy more determined and focused. Ace's legacy lives on through Luffy, and this is a common theme. Ace's values, like loyalty and protecting the weak, are also passed on to Luffy in these stories.
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, 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.
Their relationship started when they were young. Luffy was always chasing after Ace. At first, Ace was a bit annoyed by Luffy but gradually, they became inseparable. They had many experiences together on their small island. Later, even as Ace ventured out into the world with the Whitebeard Pirates, his connection to Luffy remained strong. He was always protective of Luffy, and this was clearly seen when he faced danger at Marineford to protect his younger brother.
Luffy could change the past in several ways. Firstly, he could use his devil fruit powers in a more strategic way. Since he has the experience of future battles, he knows his opponents' weaknesses better. So, when facing the enemies who were involved in Ace's capture, he can defeat them more easily. Secondly, he could try to influence Ace's relationships. Maybe he can make Ace form stronger alliances with other pirate crews, which would make it more difficult for the Navy to target him. Also, Luffy could try to expose the Navy's secret plans earlier, which would change the power dynamics in the One Piece world and ultimately save Ace.
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.
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.