A great plot could be that there's a masked vigilante hunter in Gotham who targets both Batman and Catwoman. They have to hide from this hunter while also trying to figure out who it is. Along the way, they take refuge in an abandoned part of the city and during this time of forced proximity, they have deep conversations about their motives, their pasts, and what they really want for the future of Gotham.
A cool plot could be that a powerful alien race arrives on Earth and offers a deal to the world leaders. Batman is suspicious of their motives and starts investigating. Superman, on the other hand, is more open - minded at first. This causes a rift between them. As Batman uncovers more evidence of the aliens' true intentions, he has to convince Superman. In the end, they join forces to stop the aliens from taking over the Earth.
A fanfic could explore what would happen if Catwoman found out Batman's true identity before he was ready to reveal it. Maybe she uses this knowledge to try and protect him from a threat that is specifically targeting Bruce Wayne, and in the process, their relationship takes an unexpected turn.
Perhaps Batman discovers a strange artifact that has ties to Wonder Woman's homeland. He seeks her out for help in understanding it, and together they uncover a plot by an ancient evil force that was once sealed away but is now trying to return. Their journey involves not only fighting off minions of this evil but also learning about each other's worlds more deeply.
One idea could be a story where Batman and Catwoman team up to take on a new, more powerful villain in Arkham. Maybe this villain has the ability to control the minds of the inmates, creating chaos. They'd have to use their unique skills, Batman's detective work and combat abilities, and Catwoman's agility and thieving expertise to stop the threat.
One idea could be that Batman and Catwoman have a daughter who discovers her parents' secret identities. She could struggle with the duality of their world and try to find her own place in it. Maybe she has her own unique set of skills that combine elements of both Batman and Catwoman.
One plot idea could be that Catwoman is on a heist and Batman tries to stop her as usual, but during the encounter, they share a moment where they realize their mutual attraction. They start secretly meeting up, away from the chaos of Gotham's crime world, and gradually fall in love. Another idea is that they are forced to work together to take down a common enemy much bigger than their usual foes. In the process, they see different sides of each other and their relationship deepens.
Well, perhaps a plot where Catwoman is injured during one of her heists and Batman finds her. Instead of turning her in, he takes her to his secret lair to nurse her back to health. As she recovers, they start to have long conversations about their lives and motives. This deepens their connection and eventually leads to a romantic relationship full of tension and passion, with Catwoman teasing Batman and him trying to keep his cool while being drawn to her allure.
Maybe the Joker has some information that Catwoman desperately needs. In exchange for it, she has to help him with one of his crazy schemes. Along the way, Catwoman tries to outwit the Joker and turn the situation to her advantage while still getting what she wants.
One idea could be that Catwoman steals a valuable item and Superman is tasked with retrieving it. But as he chases her, he realizes she has a noble reason for the theft, like helping the poor in Gotham. So, instead of simply arresting her, he decides to help her find a legal way to achieve her goal.
Perhaps they could start off as rivals in the fanfiction. Batman from the present is skeptical of Batman Beyond's more high - tech approach. But as the story progresses, they learn from each other and become a great team. For example, Batman could teach Batman Beyond some of his old - school detective skills, while Batman Beyond shows Batman new ways to use technology in combat and surveillance.