One interesting story could be where Joker captures Batman and tries to break his spirit by showing him a distorted Gotham City that he has created in an abandoned area. Joker might use his henchmen to taunt Batman while he's trapped, but Batman uses his wits to find a way out and turn the situation around on Joker.
In some fanfiction, when Joker captures Batman, he attempts to force Batman to reveal his true identity. He could use various psychological tactics, like showing Batman images of his loved ones in danger. However, Batman remains steadfast, and eventually, Robin or another ally manages to rescue him.
There are fanfictions where Joker captures Batman and decides to put on a 'show' for Gotham. He sets up a series of deadly traps around Batman and broadcasts it live. Batman has to not only escape the traps but also find a way to stop Joker from causing more chaos in Gotham.
One interesting story could be where Joker tries to turn Gotham against Batman in a very psychological way in the fanfiction. He spreads rumors and false evidence to make the citizens doubt Batman's motives.
You can try fanfiction websites like Archive of Our Own (AO3). There are a large number of Batman - related fanfictions on it, and you can easily search for ones where Joker captures Batman by using the search bar and typing in relevant keywords.
Well, sometimes in such fanfiction, there are alternate universes. For example, a world where the Joker and Batman have to team up against a greater evil. This flips their typical dynamic on its head and makes for an exciting read.
In some fanfictions, a plot twist could be that Batman discovers the Joker has a family or a past that explains his madness in a more sympathetic way. For example, if it's revealed that the Joker was once an ordinary man who was experimented on by a corrupt organization, and Batman has to decide whether to still see him as a pure villain or something more complex. This could change the way they interact in the story.
One idea could be that Batman captures Percy because he mistakes Percy's powers for something dangerous. Maybe he sees Percy using his water - based abilities in Gotham and thinks he's a new super - villain. Batman then has to figure out that Percy is actually from a different world and not a threat to Gotham.
Some fanfictions might focus on the psychological aspects of their relationship. The Joker's insanity and Batman's unwavering sense of justice create a really unique dynamic. In slash fanfiction, this could be explored in terms of how they understand each other on a deeper level, perhaps a level that no one else can fathom.
Another plot could involve Fem Batman and Joker in a sort of cat - and - mouse game where the Joker is specifically targeting Fem Batman because she's a woman. He might underestimate her at first, but she proves to be just as formidable as the male version. This would explore themes of gender and power in the Batman - Joker dynamic.
One interesting storyline could be Joker devising a new, elaborate plan to take over Gotham City that involves some wacky and unique traps. Batman, of course, has to use his Lego - themed gadgets and skills to stop him. Another could be a story where Joker and Batman are forced to team up against a greater threat, like a powerful alien invasion in the Lego universe. Maybe they start to understand each other a little better during this time.
One idea could be exploring a world where Batman and Joker have to team up against a greater evil. Maybe a powerful alien force arrives in Gotham and they realize they need to combine their skills, even if reluctantly.
A plot could involve the reader having a special ability that both Batman and the Joker are interested in. Batman wants to use it for the good of Gotham, while the Joker wants to corrupt it for his own amusement. The reader has to navigate between these two very different forces, and in the process, discovers more about themselves and the nature of good and evil in Gotham.