Harley's character could develop in many ways. She might become more protective and motherly, which is a big change from her usually wild and carefree self. This new - found sense of responsibility could make her question her relationship with Joker and the life of crime they lead.
Another idea is that the father of the baby is a mystery, and Harley goes on a journey to figure out who it is. Along the way, she discovers things about herself and her past relationships. This could involve her visiting old friends or foes and reminiscing about different parts of her life.
Poison Ivy might be a candidate in some creative fanfiction interpretations. Their relationship has always been very close, and if there was some kind of magical or experimental situation, Ivy could potentially be the other parent. This would lead to a very unique family dynamic and story arc.
The Joker is an obvious choice as he has a long - standing relationship with Harley Quinn in the original lore. Their complex and often toxic relationship could add a lot of drama to the pregnancy storyline.
One possible storyline could be Harley Quinn adjusting to the idea of motherhood while still dealing with her chaotic life. Maybe she's trying to figure out how to raise a child in a world full of villains and heroes. Another could be her relationship with the father of the baby, whether it's the Joker or someone else, and how that dynamic changes during the pregnancy.
In fanfiction, if Batman got Harley Quinn pregnant, it would be a huge shock to the Batman universe. It would likely create a lot of drama and conflict. Batman's moral code would be severely tested as he deals with the consequences of such an unexpected situation. His relationship with Harley Quinn would become extremely complex, and it could also affect his relationships with other characters like the Joker.
One challenge would be acceptance from their respective communities. The heroes might not accept Nightwing being involved with Harley, a former villain. And the villains might see Harley as a traitor for being with a hero. Another challenge could be protecting the pregnancy from their enemies who might want to harm them or use the baby for their own gain.
One interesting plot could be the chaos that ensues when Harley discovers she's pregnant. Maybe she tries to reform Joker into a more family - friendly person. Another could be the reaction of Gotham's villains and heroes to the news. For example, Batman might be conflicted on how to deal with a pregnant Harley who is still associated with the Joker.
There might be some out there. You could start by looking on fanfic platforms like Archive of Our Own. Sometimes they have unique takes on the relationship between Batman and Harley Quinn, and a pregnancy storyline could add an interesting twist to their dynamic.
A prevalent theme is often about relationships. It could be her relationship with the father of the child, if it's the Joker, how that dynamic changes. Or it could be about her new relationships she forms with other characters who support her during the pregnancy, like other female characters from the DC universe.