In addition to the Joker, Harley, and their baby, there could also be other characters from the DC universe making appearances. For instance, Batman might show up as he is always on the lookout for the Joker's misdeeds. He could be a threat to the family unit in the fanfiction, or perhaps an unexpected ally in some situations. Also, other villains like Poison Ivy, who is Harley's friend, could play a role. Maybe she helps Harley take care of the baby or gives advice on how to deal with the Joker's wild behavior.
One interesting plot could be the Joker and Harley trying to raise their baby in a world that is constantly against them. Maybe they have to protect the baby from other villains who want to use it for their own gains.
Well, the fanfiction could start with Harley Quinn finding out she's pregnant. The Joker is shocked at first but then decides to keep the baby as part of his 'grand plan'. As the baby grows, they have to deal with raising it in their chaotic world. Harley tries to give the baby a normal life as much as possible, while the Joker is constantly getting into trouble that puts the family in danger. It could also explore how the baby affects their relationship, whether it brings them closer or drives them further apart.
One idea could be that the baby has the Joker's chaotic nature but Harley's charm. For example, the baby might play pranks on the henchmen in a really cute yet mischievous way. Another could be that the baby has some special powers, like being able to make people laugh uncontrollably just like the Joker, but also has Harley's acrobatic skills at a very young age. Maybe the baby could be the key to a new, more 'family - oriented' life for the Joker and Harley, leading them to try and reform for the sake of their child.
The relationship can be portrayed as a journey. At first, the Joker and Harley might not know how to be parents. They could be clumsy and make mistakes. But as the baby grows, they start to adapt. The Joker might start to soften a bit, realizing that his actions could affect the baby's future. Harley would be the glue that holds the family together. She could be the one who arranges family dinners, even if it's just pizza in their hideout. The baby could also bring out a competitive side in them, like who can teach the baby the coolest trick or skill.
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.
Their relationship could potentially soften on Joker's part. Having a baby might make him see things in a different light. He might not be as cruel or reckless as before, at least when it comes to the baby. Harley, on the other hand, would be more determined than ever to keep the family together, even if it means constantly trying to reform the Joker. But at the same time, the pressure of raising a child could also lead to more fights between them as they struggle with their own issues and new responsibilities.
Their relationship could develop through shared experiences. For example, they could go on heists together and during those times, Joker could start to see Harley in a different light. He might notice her intelligence and loyalty more and more.
One great 'Joker OC Harley fanfiction' could be 'The New Face in Gotham'. It's about a new original character who gets involved with the Joker and Harley's chaotic world. The story has great character development for the OC and shows how they interact with the iconic duo.