Another aspect could be the formation of new alliances. Since Superman is evil, Batman might have to team up with other unexpected characters. For example, he could join forces with Lex Luthor, who usually opposes Superman. This would create a very different power dynamic and storyline, as they have to put aside their differences to face the greater threat of an evil Superman.
One idea could be a story where Batman and Superman have to team up to stop a new villain that has the power to manipulate time. This would force them to put aside their differences and really work together in a way they haven't before.
One idea could be a story where Batman and Superman have to team up to stop a powerful new villain who is using kryptonite - based technology. This would put Superman at a great disadvantage and force Batman to use his detective skills to find a way to neutralize the threat.
One idea could be a story where Batman and Superman's kids team up to solve a mystery in Gotham City. Maybe they find a strange device that's causing chaos and they have to use their combined skills, like Batman's detective skills and Superman's super strength, to figure it out.
One idea could be the two heroes having to hide their relationship from the public while still saving the world together. They might face challenges like dealing with their different approaches to justice within the context of their romance.
One idea could be that Batman and Superman have to team up to stop a new villain who has the power to manipulate time. This would put their different approaches to justice to the test as they race against the clock.
Here's an idea. There could be a powerful magical artifact that surfaces in both cities. It has the power to change reality. Superman, being a man of science, is initially skeptical about its power. Batman, on the other hand, has seen enough strange things in Gotham to know it's dangerous. They have to overcome their differences in beliefs as they race against time to stop different factions in both cities who want to use the artifact for their own gain. Along the way, they also learn more about each other's worlds and form a stronger bond.
In a fanfiction, perhaps there's an apocalypse scenario where Superman is infected with some kind of kryptonite - based virus that makes him go berserk. Batman has to find a cure while also keeping Superman from causing too much damage. At the same time, they are dealing with the general chaos of the apocalypse, like gangs taking over the city and other villains trying to take advantage of the situation.
One idea could be that Superman and Batman have to team up to stop a new supervillain who has the power to manipulate time. This would force them to put aside their differences and work together in a really challenging situation.
One idea could be that they team up to fight a new supervillain who has the power to manipulate time. Batman's detective skills and the female Superman's super strength would make for an exciting combination.
Another plot could be that Batman discovers a new weakness of Superman. Perhaps it has something to do with a certain frequency or energy that Superman is vulnerable to. Batman then builds a device that emits this energy, and during their battle, he uses it to incapacitate Superman. This would be a unique take on the 'Batman defeats Superman' scenario.