One popular storyline could be them teaming up against a common enemy that is too powerful for either of them alone. For example, a new super - villain who has the power to manipulate time. They have to combine their skills, Batman's detective skills and Superman's super strength and flight, to figure out how to defeat this villain. Another storyline might involve them having a falling - out over their different methods of protecting the city, and then having to reconcile in order to save the world from a cataclysmic event. There could also be a story where they discover they are long - lost brothers in a more in - depth way, exploring their family history and how it impacts their relationship.
A great storyline is when they face an alien invasion. Batman uses his strategic mind to plan defenses on the ground while Superman battles the alien forces in the air. Their brotherly bond is tested as Superman is tempted by the aliens to join them, believing they can bring peace in a more 'efficient' way. Batman has to convince Superman of the true nature of these aliens. It shows their different perspectives but also how they rely on each other. Another is when they travel to an alternate dimension together where their roles are reversed, and they learn to appreciate each other's strengths more.
A very common plot in such fanfiction is the origin story of their brotherhood. It could involve some secret history of their families or a hidden prophecy. Also, there are storylines where they have a falling - out as brothers, maybe because of a misunderstanding about their powers or their roles. But then they reconcile and become stronger together. There are also stories where they discover new powers or abilities because of their brotherly connection.
One interesting storyline could be a team - up against a powerful new villain that neither can defeat alone. They have to combine their unique skills, like Superman's super strength and Batman's detective skills.
In some Mpreg fanfictions, there could be a storyline where Batman and Superman have to figure out the genetics of their unborn child. Given their different origins - one being a Kryptonian and the other a human with no super - powers originally - it would be fascinating to see how their child might inherit or combine their abilities. There could also be a plot where they have to deal with time - traveling villains who try to prevent the birth of their child for some evil purpose.
A cool story could be about them having a friendly competition to see who can solve a series of mysterious crimes in the other's city first. Along the way, they learn more about each other's methods and develop a deeper respect for one another. This also gives an opportunity to explore the different atmospheres and challenges of Gotham and Metropolis.
One interesting storyline could be a young Superman and Batman teaming up for the first time in a kid - friendly adventure. Maybe they are trying to stop a group of small - time villains who are stealing toys from all the kids in Gotham. They use their unique powers and detective skills respectively to track down the bad guys and return the toys.
One interesting storyline could be them teaming up against a new supervillain that neither can defeat alone. They combine their unique skills, Superman's super strength and flight with Batman's detective skills and gadgets.
One interesting storyline could be a redemption arc for Superman. In the Injustice universe, Superman has gone down a dark path. A fanfiction might explore how Batman tries to bring back the good in him, with lots of emotional confrontations and moral debates between the two.
There are fanfictions that focus on their early days. Maybe a young Bruce Wayne meeting a young Clark Kent and how their initial encounters shape their future relationship as the Dark Knight and the Man of Steel. It could be about how they learn from each other, with Clark teaching Bruce about hope and Bruce teaching Clark about strategy.
Well, in batman and superman fanfiction, a common theme is the exploration of their dual identities. How Batman's Bruce Wayne and Superman's Clark Kent interact with each other on a personal level outside of their superhero personas. Also, time - travel plots are quite popular, where they might go back in time to prevent a major disaster that affects both of them. Some fanfictions also focus on the love interests of these two heroes and how that can create interesting storylines.
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.