Obviously, Harry would be the central character. He's the one seeking revenge. Hermione would also likely be involved. She might be torn between her loyalty to Harry and her belief in the Order. If she sides with Harry, she could use her intelligence to help him in his revenge plot, like coming up with elaborate plans to outwit the Order. Ron could also play a significant role. He might initially be against Harry's idea of revenge but then slowly come around as he realizes Harry's reasons.
Dumbledore, even if he's not alive in the story, could still be a key character in a way. His past actions and decisions regarding the Order could be the root cause of Harry's revenge. Harry might be uncovering things that Dumbledore did that he feels are unjust. Snape is another character who could be important. His past relationship with the Order and his complex history with Harry could add more layers to the story. If the fanfiction delves into the darker side of the Order, Snape's knowledge of their secrets could be a crucial part of Harry's revenge.
Perhaps Harry finds out that the Order has made a deal with someone he doesn't trust. In his revenge, he could expose this deal to the wizarding community. He'd use his influence as the Boy Who Lived to make sure the public knows. He might gather evidence and present it in a very public way, like during a big wizarding event. This would not only embarrass the Order but also make them lose the trust of many wizards and witches who previously supported them.
Harry and Ron could be her obvious allies. They've been through so much together, and if Hermione has a reason to get revenge on the Order, they'd likely stand by her side. They trust her judgment and would be willing to help her out.
She might get revenge because she felt the Order made a decision that put her or her friends in danger. For example, if they sent Harry on a dangerous mission without proper support, Hermione could plan some elaborate scheme to teach them a lesson. Maybe she'd use her intelligence to expose some of their secrets or weaknesses.
Obviously, Harry himself is a key character. His own strength, both physical and mental, could play a role in his release. For instance, he might have developed some new magical abilities during his time in Azkaban that help him break free.
Ron might support Harry at first. Since he's Harry's best friend, he would be on Harry's side without really knowing the full story. He'd probably offer to help Harry with some of his revenge plans, like distracting Ginny while Harry sets up a magical prank.
His friends from Hogwarts like Ron and Hermione. They are always by his side and would probably be more than happy to help Harry get revenge on the Dursleys. They might use their magic skills together to create some really interesting revenge scenarios.
Obviously, Harry Potter himself is the central figure. His friends like Ron and Hermione would also be involved. They would support Harry in his revenge plans, with Ron providing his loyalty and Hermione using her intelligence to strategize. Ginny Weasley might also be part of it, as she is Harry's love interest and a strong - willed witch in her own right.
His friends like Ron and Hermione could be his allies. They have always stood by Harry and if Harry believes that Dumbledore has wronged him, they might side with him. Ron, with his loyalty and Hermione with her intelligence could help Harry plan and execute his revenge. They could use their knowledge of magic and Hogwarts to find ways to undermine Dumbledore's influence.
Maybe Ginny did something that Harry thought was a betrayal, like siding with someone against him in a wizarding conflict. So Harry decides to play some harmless pranks on her to get revenge. For example, he might use magic to make her quill write silly things during a class.
Maybe Harry uses magic to make their house a mess. He could turn Dudley's room into a pigsty or make Aunt Petunia's precious china float and then smash. It's his way of getting back at all the years of mistreatment.