One idea could be a story where Batgirl has to save Batman from a new and powerful villain. Maybe this villain has a special weapon that can neutralize Batman's skills, and Batgirl uses her unique abilities, like her gymnastic skills and her knowledge of technology, to turn the tables.
A fanfic could focus on the relationship between Batman and Batgirl. For example, exploring how Batman trained Batgirl and how their mentor - mentee relationship evolved over time. It could also show how they handle their differences in combat styles and decision - making during a big mission in Gotham City.
Another interesting fanfic could be set in an alternate universe. In this universe, Batman is a young rookie and Batgirl is his more experienced mentor. It would be a role - reversal story where Batgirl teaches Batman the ropes of fighting crime in Gotham. This could include her showing him how to use his gadgets more effectively and how to read the criminal underworld better.
A story about a mystery that only their combined efforts can solve. For instance, there are a series of strange disappearances in Gotham that seem to be related to an ancient cult. Batman uses his detective skills, Batgirl her research abilities and Catwoman her street - level contacts to piece together the clues. Or perhaps a story where they must protect a powerful and dangerous artifact from falling into the wrong hands. They have to put aside their differences and trust each other to succeed.
Perhaps a plot where Batman and Batgirl are investigating a series of strange disappearances in Gotham. They find out that it's related to a secret underground organization that is using some sort of new technology. Along the way, they start to realize their feelings for each other are deeper than just being crime - fighting partners. But they have to put their personal feelings aside to stop the organization before it's too late.
Perhaps there could be a storyline where the baby is actually a key to saving Gotham in the future. Batman and Batgirl discover this and have to raise the baby in a way that will prepare it for its important role. They face many challenges along the way, including trying to keep the baby's identity a secret from their enemies.
One idea could be exploring Batgirl's internal struggle after the events of 'The Killing Joke'. Maybe she has nightmares and has to face her own fears in a new way. Another could be Batman's reaction to Batgirl's changed state of mind, and how he tries to help her without being too overbearing.
One idea could be Batgirl Beyond facing a new high - tech villain who has the ability to hack into the city's entire infrastructure. She has to use her wits and upgraded gadgets to stop him before he shuts down power and communication across the city.
One idea could be exploring Batman's early days as a vigilante in more detail. Show his first encounters with the major villains and how he developed his crime - fighting techniques.
A cool plot could be that there's a mysterious threat targeting all of Batman's allies. Robin and Batgirl team up to not only find out who's behind it but also to protect each other. Along the way, they share some personal stories from their pasts that bring them closer together.
A really cool storyline could be a time - travel one in the fanfiction. Batman, Robin, and Batgirl are sent to the past or future Gotham. In this new time period, they have to adapt to different versions of the city and its threats. Robin might be especially fascinated by the differences in technology and crime - fighting methods, and together they work to find a way back to their own time.
Another storyline might involve Batgirl getting into a difficult situation where Batman has to rescue her, and then they train together to make sure she's better prepared for future threats. This could show their mentor - mentee relationship evolving into a more equal partnership. For example, Batman could teach her some advanced combat techniques and Batgirl could share her insights on dealing with certain types of criminals that Batman might not be as familiar with.