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.
Lex Luthor is often an interesting character in such fanfictions. He might be the one pulling the strings behind the scenes, fueling Batman's distrust of Superman. Another could be Alfred. His wisdom and influence on Batman can add depth to the story. He might try to talk Batman out of fighting Superman or help him in a more covert way. And then there's Wonder Woman. She could be caught in the middle, trying to mediate between the two or having her own motives for getting involved in their conflict.
Catwoman can also be a popular character. She could be in a love - triangle situation with Batman, and her thieving ways might put her at odds with the female Superman who stands for truth and justice. There could be some really interesting interactions between the three of them, like Catwoman trying to steal a valuable item that the female Superman is protecting, while Batman is caught in the middle, not sure who to side with at first.
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.
Often it starts with mutual respect. They recognize each other's abilities and dedication to justice. For instance, Superman respects Batman's ability to fight crime without powers, and Batman respects Superman's selfless use of his powers.
Then there's 'MetropolisMuse'. They are known for their fanfictions that explore the more human side of Superman and how his relationship with Batman is affected by his dual identity as Clark Kent. Their writing style is very emotional and engaging.
Determining the best authors in batman and superman fanfiction is no easy feat. Some authors like 'BatmanFanatic' are great at creating complex plotlines that involve both heroes and their rogues' galleries. They keep the readers on their toes with unexpected twists and turns. 'SupermanLover' is another author who is known for her detailed descriptions of Superman's powers and how they interact with Batman's gadgets. Additionally, there are those who collaborate on fanfictions, and these collaborative works often bring out the best of different writing styles and ideas.
One possible reason could be mind control. Maybe some villain has taken over Superman's mind and made him do it. Another reason might be a fundamental difference in their ideologies that has escalated to the point of no return.
Alfred is always a likely ally. His knowledge and experience can provide valuable support to Batman. Also, Oracle (Barbara Gordon) could be an important ally, using her hacking skills to disrupt any technology Superman might use or to gather information.