Well, in this fanfiction, Luffy could interact with the Marines in a more diplomatic way. Since he has the advantage of time travel, he might understand the reasons behind the Marines' actions better. So, he could try to negotiate or make deals with some of the more reasonable Marines. He could offer to help them with other threats in the One Piece world in exchange for them leaving his friends alone at Marineford.
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.
One interesting storyline could be Ace and Luffy teaming up against a powerful marine squadron. They might use their unique abilities, like Ace's fire powers and Luffy's stretchy attacks, to outwit the marines. Another could be a story where Luffy tries to rescue Ace from a high - security marine prison, facing many challenges along the way.
In fanfiction, a recurring storyline is the Marines' attempts to undermine the brotherly bond of Luffy, Ace, and Sabo. They might try to spread false rumors or create misunderstandings between them. Another popular one is the story of a Marine defector who joins Luffy's crew after realizing the corruption within the Marine ranks. Also, there are stories that focus on the power - up of Luffy, Ace, and Sabo in relation to the Marines. For example, they might gain new abilities and then use them to outwit the Marines in a big battle. There could also be fanfictions that explore the emotional side of the Marines, like a Marine who feels guilty for having to fight against the brothers because he secretly admires their loyalty to each other.
Obviously, Ace and Luffy are the most popular. But other characters like Zoro from Luffy's crew are also often included. On the marine side, characters like Smoker are quite popular as he has a sort of grudging respect for Luffy. Also, Akainu is often included as the big bad marine that Ace and Luffy have to face off against.
The consequences can be quite complex. Firstly, Harry might report her to the relevant authorities in the fanfiction world, like the magical law enforcement. This could lead to her facing legal penalties. Emotionally, Harry could be deeply hurt and become more guarded in future relationships. His friends might also side with him, leaving Molly isolated. Moreover, it could change the power dynamics in the story, as Harry might gain more sympathy from others, while Molly's reputation takes a huge hit.