Obviously, Harry Potter himself is the main character as he is the one getting back at the Dursleys. The Dursleys - Uncle Vernon, Aunt Petunia, and Dudley - are also main characters as they are the targets of Harry's revenge.
The main character is Harry Potter, no doubt. He has endured so much from the Dursleys that he decides to take action. The Dursleys are also key characters. Their overbearing and cruel behavior towards Harry is the reason for his retaliation. Additionally, there could be other characters from Hogwarts who might make an appearance in the fanfiction. For instance, Hermione Granger could offer some smart ideas to Harry on how to get back at the Dursleys in a more clever and less detectable way. Ron Weasley could also be there, providing some moral support or comical reactions to Harry's revenge plans.
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 is one of the main characters. He is the one who is being accepted by the Dursleys. Then there are the Dursleys themselves - Vernon, Petunia, and Dudley. Vernon is the strict and often grumpy uncle, Petunia is the aunt who has always been envious of Lily (Harry's mother), and Dudley is the spoiled cousin. Their interactions with Harry will be central to the story as they shift from their previous negative attitude towards acceptance.
Obviously, Harry Potter himself is the main character. He is the one with the motivation to fight against the Dursleys due to their years of mistreatment.
The main characters would be Harry Potter without a doubt. Since he is the focal point of the story as he is chained up. The Dursleys are key characters too. Vernon Dursley, with his mean - spirited nature, Petunia, who has always been cold towards Harry, and Dudley, who might have a change of heart during the story. And of course, we can't forget about Hedwig. She could be a crucial character, perhaps trying to bring help to Harry or at least provide some comfort while he is in such a dire situation.
Hermione would likely be one of the characters. She's Harry's best friend and would probably try to find him and help him out. Ron might also be there, as he's always been by Harry's side. Dumbledore could be another character. He might be trying to keep an eye on Harry from afar, or perhaps he has a plan for Harry's new situation. Hagrid would also be a likely character. He has a soft spot for Harry and would want to make sure he's okay. And of course, the Dursleys themselves might make appearances, either to continue their mean - spirited ways or to have a change of heart.
Jaime is the main character without a doubt. But other important characters could include the maesters. They might be the ones attempting to use their medical knowledge or ancient lore to figure out how to restore his hand. And Cersei is likely to be in it too. Her reaction to Jaime getting his hand back, whether it's relief, jealousy or something else, will add to the story. And don't forget about Bronn. He might be involved in some of the more dangerous or practical aspects of Jaime's quest to get his hand, like providing protection or finding necessary items.
Well, perhaps Harry would start by making the Dursleys' house a bit of a chaos. He could make the stairs creak whenever Uncle Vernon is trying to sneak around, or make Aunt Petunia's precious china rattle whenever she is being particularly mean. He might also use magic to make Dudley's new clothes look like old rags in front of his friends, which would be quite embarrassing for him.
Obviously, Harry's kids would be the main characters. They could be the ones driving the story forward with their curiosity about their father's past and the Dursleys. And of course, the Dursleys themselves. Vernon, Petunia, and Dudley. They are important as they are the connection to Harry's difficult childhood. Their reactions to the kids would be a major part of the story.
Depending on the plot of the 'harry gets even fanfic', some other characters from the Harry Potter universe might make an appearance. For instance, Professor Dumbledore, even though he's passed away in the original series. His wisdom might be a guiding force for Harry, either through memories or some kind of magical connection. Or characters like Luna Lovegood could also be involved, perhaps providing some unique perspective on Harry's need for revenge.
Draco would surely interact with the Dursleys. Vernon would probably be very suspicious and hostile towards Draco at first, seeing him as another strange and magical being. Petunia might be a bit more reserved but also curious in her own way. Dudley could range from being intimidated by Draco's wizarding background to being fascinated. And don't forget about Hedwig! If she's still around, Draco might have some sort of interaction with the owl, which could be really funny or interesting as he tries to figure out how to deal with this magical creature in the Muggle - dominated Dursleys' household.