Perhaps a fanfiction where Catwoman finds a mysterious item in Arkham during one of her heists. This item has some sort of strange power that attracts the attention of Batman. They both end up on a quest to figure out what the item is and where it came from. Their relationship would be tested as they face various obstacles and other characters who also want the item for their own purposes.
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.
A plot could involve Catwoman getting framed for a crime she didn't commit within Arkham. Batman doesn't believe she's guilty and sets out to prove her innocence. Along the way, they discover a conspiracy within Arkham's walls that involves some of the staff. This would lead to a lot of tense moments as they try to expose the truth while avoiding getting caught by the real culprits.
In this fanfiction, it could be interesting if Catwoman discovers a secret about the Arkham Knight that Batman has overlooked. She could use this knowledge to her advantage, either to make a deal with the Arkham Knight or to help Batman. For example, she might find out that the Arkham Knight has a weakness related to a certain location in Gotham that was important to his past. Catwoman could then lead Batman there to take down the Arkham Knight.
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.
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.
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 idea could be exploring the backstories of the lesser - known characters in the 'Batman Assault on Arkham' universe more deeply. For example, you could focus on Killer Croc's life before Arkham and what led him to become the way he is. Another plot could involve a team - up between unexpected characters from the movie, like Harley Quinn and Deadshot, against a new threat in Arkham that the Bat - family is unaware of.
One idea could be exploring a new villain in Neo - Gotham. Maybe a tech - based criminal who can hack into the Bat - suit's systems, creating a whole new set of challenges for Terry McGinnis. Another could be a story where Terry has to team up with an old - school Batman villain who has somehow resurfaced in the future, like the Riddler, but with a new high - tech twist on his riddles.
Well, you could write a fanfiction where the Joker somehow returns in Arkham Beyond, but he has a new, more terrifying form. Batman must figure out how this is possible and stop him before he causes even more mayhem. Or perhaps a story centered around Harley Quinn trying to redeem herself in the Arkham Beyond setting. She could team up with Batman to take down a common enemy, which would create an interesting dynamic between the two characters.
In some fanfictions, the plotline might be that there's a hidden treasure in Arkham City that both Batman and Catwoman are after for different reasons. They start as rivals but as they face the various threats in Arkham City, like the other inmates and the corrupt guards, they realize they need to work together. This story could explore how they negotiate their differences and build a stronger bond in the context of Arkham City.
You could also do a 'what if' scenario. For instance, what if Batman had to team up with some of the Arkham inmates, like Harley Quinn and Poison Ivy, to stop a greater threat that was endangering not only Gotham but also the inmates' own lives? This would involve exploring their complex personalities and how they might interact with Batman in a different context.
Perhaps in the Young Justice universe, Catwoman discovers a secret about Batman's past that puts her in a moral dilemma. She could either use this information to her advantage or help him keep it hidden. As they interact more because of this, feelings start to develop between them that they didn't expect. They have to navigate their relationship while also dealing with the threats that Young Justice faces.