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.
Some fanfics might explore an alternate universe where their roles are different. For instance, Robin could be a powerful mage like Tharja, and they bond over their shared magical abilities. Or perhaps they are from different kingdoms originally and their relationship has to navigate the politics between the two kingdoms while also dealing with their growing feelings for each other. This can lead to a lot of complex and interesting storylines.
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 that Christopher Robin gets lost in the Hundred Acre Wood as an adult and Pooh has to help him remember all the wonderful things from his childhood. They could go on a journey to find the special places that they used to visit together, like the bridge over the stream or the bee tree.
A cool plot idea could be that the child has a unique power that neither Robin nor Raven have. This power could attract the attention of an ancient evil force that was once sealed away. So, Robin and Raven have to team up with their friends to not only protect their child but also the whole world from this new threat.
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.
One idea could be that the OC is a new vigilante in Gotham and Batgirl takes them under her wing to train them. This could lead to a lot of action - packed scenes as they fight crime together and the OC learns from Batgirl's experience.
One plot idea could be that Supergirl and Batgirl team up to take on a new super - villain in Gotham. This villain has the ability to manipulate technology and is causing chaos. They combine Supergirl's super strength and flight with Batgirl's detective skills and martial arts expertise. Another idea is that they are transported to an alternate dimension where they have to find a way back home while facing different versions of their friends and foes. And a third idea could be that a powerful alien artifact is found in Metropolis and both girls must protect it from various forces that want to use it for evil, all while learning more about each other's worlds and abilities.
Maybe the OC is from a long - lost island with unique knowledge. Robin is interested in the historical aspects of this knowledge and Nami sees the potential for great treasures. The OC then has to deal with the different personalities of Robin and Nami. Robin is calm and intellectual, while Nami can be feisty. Their interactions lead to a series of adventures and a deepening of their relationships.
One idea could be that Robin gets trapped in an alternate dimension where the villains are in control and Batman has to figure out a way to bring him back. Another could be a story where Batman is injured and Robin has to take on a major villain alone, learning to trust his own instincts more. Maybe a plot where they encounter a new, powerful ally who turns out to have a hidden agenda that threatens Gotham.
A plot idea could be Robin's pregnancy being a surprise not just to her but also to her family. Her family might have different reactions, some being very supportive while others might be disappointed or worried. The fanfic could then show how Robin overcomes these family issues while also dealing with the physical and emotional changes of pregnancy. Or it could be about Robin's pregnancy in a world where she has some sort of special ability or power, and how the pregnancy affects that ability and how she has to protect herself and the unborn baby from those who might want to take advantage of her situation.