Catwoman might be in the story too. She could be interested in the situation, especially if it affects her criminal activities in Gotham. She might try to use the confusion caused by the two Batmen to her advantage, or she could end up getting caught in the middle of their conflict and have to choose a side.
Alfred Pennyworth could be involved. He could be the voice of reason when the two Batmen start to clash. He might try to mediate between them and remind them of their common goals. Also, Commissioner Gordon could be there. His reaction to two Batmen would be interesting, and he could play a role in getting them to work together against the criminals in Gotham.
Wonder Woman could also be involved. She might be caught in the middle, trying to stop the fight at first. But if she realizes that Superman is being a threat for some reason, she could side with Batman, or at least not interfere in Batman's attempt to defeat Superman.
Well, obviously the two main characters are Batman from the normal DC universe and Flashpoint Batman. Batman is the well - known Dark Knight, a symbol of justice in Gotham. Flashpoint Batman is from an alternate timeline, with different experiences and a potentially different personality.
The Mayor could be a key character. He might be the one promoting Batman's image in the city, seeing him as a way to boost morale. Also, there could be a journalist who is always trying to get the inside scoop on Batman and in the process, shows the city's fascination with him.
A new tech - savvy villain who is a master of hacking could be introduced. This villain could pose a threat to both Batmen as they rely on technology in different ways.
Robin is a very popular character. He has a close relationship with Batman, and in fanfiction, their bond can be explored in different ways, like how Robin influences Batman's decisions. Another is The Joker. His chaotic nature makes for interesting interactions with Batman in these stories.
Robin could be a great addition. He could act as a bridge between Starfire's more light - hearted nature and Batman's seriousness. His acrobatic skills and detective training could complement both of them in a fight. Another good character would be Nightwing. He has a connection to Batman already and his charm could add an interesting element when interacting with Starfire.
Alfred would be a great addition. He could offer his wisdom and support to Batman and Batgirl's relationship, and also provide some much - needed comic relief. Another good character is Commissioner Gordon. His connection to the Bat - family and the police force could add an interesting dynamic to the story, especially if he has to deal with the relationship between Batman and Batgirl in some way.
Lois Lane is often a popular character. In fanfiction, she might play a crucial role in mediating between Batman and Superman or getting involved in their adventures in a more hands - on way, using her investigative journalism skills.
Alfred Pennyworth is quite popular too. He can offer his wisdom and support to Batman, and his interactions with Superman can be both humorous and heartwarming. He's like the glue that holds things together in the Batcave, and his presence can bring a sense of home to the story.
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.