The other members of the Bat - family like Robin, Nightwing, and Batgirl are likely to be main characters too. They would be involved in filling the void left by Batman in protecting Gotham.
Obviously, Batman himself would be one of the main characters. And of course, his parents, Thomas and Martha Wayne. There could also be Alfred, as he is an important figure in Batman's life and might play a role in facilitating the meeting or providing some insights afterwards.
One idea could be exploring how Batman's allies step up in his absence while he's recovering from a broken back. For example, Robin might take on more responsibilities in protecting Gotham.
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.
Obviously, Nightwing himself would be the main character as he's the one taking on the Batman role. Robin, if there's a younger Robin at the time in the fanfiction, would also be a key character. He might look up to Nightwing in his new role or have some doubts about him filling Batman's shoes.
Most likely, Sam and Dean Winchester would be main characters. They are the central figures in the Supernatural series, and any fanfiction set in that universe would probably revolve around them. They are the ones who usually deal with the chaos and the supernatural threats.
Obviously, Batman would be one of the main characters. And of course, the other members of the Justice League like Superman, Wonder Woman, Flash, Green Lantern, etc. would also be important. There might also be some villains that are central to the story, such as Lex Luthor who could be plotting against the newly - formed alliance of Batman and the Justice League.
In addition to Batman, Superman, and Wonder Woman, The Flash could also be a main character. His super - speed would add an element of quick - paced action and his humorous personality would provide some levity. Aquaman, with his connection to the ocean and his trident, is also likely to be a main character. He can bring in a different perspective, especially when it comes to underwater or environmental threats. Green Lantern, with his power ring and willpower, would also be important as he has unique abilities that can be used in various ways to fight threats.
Obviously, Harry and Sirius are the main characters. Harry is the one trying to break Sirius out, and Sirius is the one being broken out.
Obviously, Batman himself would be one of the main characters. And his son, who could be Damian Wayne, for example. There might also be Alfred, as he is often involved in the Bat - family's affairs and could be present during or contribute to the talk in some way.
Batman's allies such as Commissioner Gordon could be involved. Sometimes Batman might be angry at Gordon if he feels that the police force is not doing enough to support his fight against crime. Also, other members of the Bat - family like Batgirl could be part of the story. Their actions or decisions might trigger Batman's anger. For instance, if Batgirl decides to take on a powerful villain alone against Batman's advice.