A possible plot could be that Harley discovers she's pregnant right after a big fight with Joker. She's not sure if she wants to keep the baby at first, but as time goes on, she realizes she does. Meanwhile, Joker is off on his own misadventures and when he finds out, he has to decide if he's ready to be a father. This could create a lot of tension and also some really sweet moments between them as they figure out their new roles.
One idea could be that Harley tries to hide her pregnancy from Joker at first because she's not sure how he'll react. Another could be that they go on a wild adventure while Harley is pregnant, facing various villains who either try to use her condition against them or are unexpectedly helpful. Or perhaps there's a plot where Harley has to deal with her own insecurities about becoming a mother while still being in a relationship with the unpredictable Joker.
One plot idea could be the Joker trying to prove his love to Harley in a really extreme way, like taking over Gotham City and dedicating it to her. It shows his over - the - top and crazy way of loving.
One idea could be a story where Harley Quinn tries to break free from the Joker's control completely and starts her own life of crime without him. She could form her own gang and prove that she's more than just the Joker's sidekick.
One idea could be that the OC is a new villain in Gotham who catches the attention of both Joker and Harley. Maybe the OC has a unique power or skill that makes them a threat or an ally. For example, the OC could have the ability to manipulate minds, which Joker wants to use for his own evil plans, while Harley sees the OC as a potential friend who can understand her chaotic nature.
One idea could be that Harley Quinn and Joker have a baby, and the baby inherits their chaotic and unpredictable nature. Maybe the baby starts causing mayhem in Gotham from a very young age, and the other villains and heroes are all shocked and don't know how to deal with this new situation.
One plot idea could be Harley trying to break free from the Joker's control in a more psychological way. Maybe she starts having dreams that show her a different life without him, and she begins to question their relationship while still being in love with him. Another idea is a story where the Joker and Harley team up with other villains from the Dark Knight universe against a common enemy. For example, they could join forces with Bane to take over Gotham, but there are internal power struggles within their alliance.
A third plot could involve an external force trying to break them apart. Maybe a rival criminal or a vigilante realizes that Harley is Joker's weakness and tries to use that to their advantage. This would force Joker and Harley to work together in a new way to stay together and fight off the threat.
For a joker and harley lemon fanfiction, you could write a story where they get lost in a magical forest. In this forest, they have to face their inner demons together. Harley could use her charm and wits to help Joker deal with his insecurities, and in the process, their relationship deepens. You could also explore a scenario where Joker is injured and Harley has to take care of him. This would show a different side of their relationship, a more tender side. Additionally, a story about them stealing a precious artifact from a powerful villain and how they celebrate their victory with some passionate moments could be interesting.
Another plot could be a role - reversal. The Joker gets hit by some strange gas that makes him lose his 'evil' side for a while. Harley then has to deal with a very different Joker, and she starts to miss the old him in some ways while also enjoying this new side of him. It could be a story of self - discovery for both of them.
One idea could be that the OC is a new villain in Gotham who catches the Joker's attention. He decides to use the OC to make Harley jealous, which then leads to a complex love - triangle - like situation full of drama and chaos.
One idea could be Harley Quinn trying to break free from the Joker's control completely within the Suicide Squad setting. Maybe she starts to form real friendships with the other Squad members, like Deadshot, and they help her see that she doesn't need the Joker's madness in her life.