Lois Lane is a must - include. She can be the love interest and also a strong - willed journalist. Jimmy Olsen is also great, providing some comical relief and being Superman's friend. Lex Luthor is an obvious choice as the main villain, always plotting against Superman.
Lex Luthor is another key character. He has a complex relationship with Superman. In the context of the 'Death of Superman' novels, his actions and reactions to Superman's death are significant as he is often an antagonist who might have mixed feelings about the situation.
Jimmy Olsen could also be a great character to include. He is Superman's friend and colleague at the Daily Planet. His loyalty and his ability to get into some sticky situations can add a touch of humor and also some interesting sub - plots to the Supergirl and Superman fanfiction.
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.
Superman, of course, is the most important. Then there's Lois Lane, the journalist who is always on the hunt for a story and has a special relationship with Superman. Lex Luthor is also crucial as the main antagonist.
Obviously, Superman himself is the most important. He is the hero with superpowers. And Lois Lane is also important as she is often in the middle of the stories and has a relationship with Superman.
One idea could be having Superman face an enemy that can manipulate time, causing chaos in Metropolis. Another could be a story where he has to deal with a powerful alien artifact that is affecting his powers. Maybe also a plot where he teams up with a new superhero from another planet.
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.
Often, there could be other superheroes or villains. For instance, Lex Luthor might make an appearance. He could either be an ally to the reader in trying to stop the evil Superman or have his own ulterior motives for getting involved. Another character could be Lois Lane. She might be used as a plot device, perhaps the reader has to protect her from the evil Superman or she could be a source of jealousy for the evil Superman if he has feelings for the reader.
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.