One possible plot could be that they team up to stop a powerful alien threat that is beyond what Supergirl can handle alone. Batman's strategic mind would be crucial in devising a plan to take down this foe. Maybe they have to find a way to combine Supergirl's superpowers with Batman's gadgets and combat skills.
Well, perhaps there's a new villain in town who has the ability to disrupt all forms of communication and technology in Gotham and Metropolis simultaneously. Supergirl and Batman team up because they realize that neither can solve this problem on their own. Supergirl can use her super - senses to try and track the source of the disruption, while Batman uses his detective skills to analyze the patterns of the attacks. They might also have some interesting interactions along the way, like Supergirl being amazed at Batman's determination despite not having any superpowers, and Batman being in awe of Supergirl's raw power.
Supergirl is generally more optimistic and believes in the good in people. Batman, on the other hand, has seen the worst of humanity and is often cynical. This could lead to some clashes. But it can also be a great complement. Supergirl's optimism can help Batman see the better side of things sometimes. And Batman's caution can prevent Supergirl from making hasty decisions. In a fanfiction, we could see this play out when they are dealing with a villain who claims to have reformed. Supergirl might be inclined to believe them, while Batman would be looking for signs of deception.
A plot could involve a time - travel scenario where Batman and Supergirl are sent back in time to prevent a major event that would change the future of both their worlds. They would have to work together, using their different skills and knowledge of their respective eras.
In a 'Team Flash meets Supergirl' fanfiction, there could be an epic team - up. The Flash might use his super speed to save Supergirl from a kryptonite - powered trap. Then they could join forces to fight a common enemy like Lex Luthor or an alien invasion. The scientific minds in Team Flash could also help Supergirl understand some new aspects of her powers.
One idea could be that Batman tries to train Supergirl to better control her powers in the context of the Injustice 2 universe. He might see her as a potential force for good against the tyrannical regime. Another could be that Supergirl discovers a way to bring back the more heroic Superman she once knew, and Batman has to decide whether to trust her plan or not.
One idea could be that Supergirl and Batman team up to stop a powerful alien weapon from being used on Earth. Maybe the weapon was stolen from a Kryptonian ship and Batman uses his detective skills to find clues while Supergirl uses her superpowers to fight off the bad guys who have the weapon.
Supergirl's exuberance and her willingness to trust can sometimes clash with Batman's more cynical view. However, in the context of a romance in fanfiction, this can be a source of growth for both of them. Batman might start to trust more because of Supergirl, and Supergirl might become more cautious under Batman's influence. Their personalities also play a role in how they show affection. Batman might be more reserved in his displays, while Supergirl could be more open and affectionate, which could lead to some sweet and sometimes awkward moments as they navigate their relationship.
Well, their team - up would be amazing. Spider - Man's acrobatic skills and web - slinging along with Supergirl's super strength and flight could make for some really cool action scenes. They could fight villains that neither could handle alone. For example, a powerful alien who can resist Spider - Man's physical attacks but is vulnerable to Supergirl's heat vision, and at the same time, Supergirl might need Spider - Man's quick thinking and agility to deal with the villain's minions.
The plot could involve a new villain in Gotham who has a technology that can control people's minds. This villain starts to turn the citizens of Gotham against each other. Batman realizes that he needs the Joker's unique brand of chaos to break the pattern of the mind - control. The Joker, on the other hand, sees this as an opportunity to create even more mayhem. They join forces, with Batman trying to direct the Joker's actions to some extent. As they fight the villain, the Joker may come up with some out - of - the - box ideas to disable the mind - control device, while Batman focuses on protecting the innocent. But of course, their alliance is fragile, and at any moment the Joker could turn on Batman.
In a 'Harry Potter and Voldemort team up' fanfiction, the plot could involve a prophecy that states only the combined power of the two can save the wizarding world from an upcoming cataclysm. At first, they are reluctant, but as the signs of the impending doom become more evident, they put aside their differences. They use their combined magic to unlock ancient secrets and find magical artifacts that are needed to prevent the disaster. This new alliance also causes a major shift in the power dynamics and relationships within the wizarding world.
One possible plot could be that they have to team up to stop an ancient evil that is rising. Each of them brings their own unique powers to the table. Percy with his control over water, Jason with his power over the wind and lightning, and Nico with his ability to manipulate the shadows. They journey to different realms to find the artifacts needed to defeat this evil.