A great plot could be Nightwing taking them on a mission away from Gotham. They end up in a small town where they have to solve a mystery that is not related to the typical Gotham villains. This forces them to rely on each other more and also gives Nightwing a chance to bond with them in a different environment. Maybe they have to deal with a cult that is trying to sacrifice the town's people. Nightwing would lead the way, but also let Jason, Tim and Damian take charge at different points to build their confidence.
One plot idea could be Nightwing teaching them his unique combat skills. He could have a special training session where he combines his acrobatic fighting style with elements from each of their own combat preferences. For example, incorporating Jason's more brute force when necessary, Tim's strategic thinking, and Damian's precision. Another idea is Nightwing helping them deal with their personal demons. He might sit down with Jason and talk about his past traumas and how to move forward. With Tim, it could be about his insecurities in the Bat - family. And for Damian, Nightwing could guide him on how to better fit into the family and society outside of just being a warrior.
Nightwing would likely be more empathetic with Jason. Given Jason's troubled past, Nightwing would be patient and understanding. He'd probably let Jason vent his frustrations and anger in a safe way. With Tim, Nightwing might be more of a mentor in terms of detective work. He'd share his knowledge and experiences to help Tim grow in that area. For Damian, Nightwing would be firm yet gentle. He'd enforce rules but also make sure Damian feels like part of the family and not just an heir to be molded.
One interesting fanfiction could be where Nightwing takes on the role of Damian's mentor in a very strict yet loving way. He teaches Damian not just combat skills but also about morality and friendship. In this story, they might go on adventures together, facing villains that force Damian to grow under Nightwing's guidance.
A plot could involve a dark future where Jason and Tim are on opposite sides of a war in Gotham. The city has been overrun by a new, powerful villain. Tim is still trying to uphold the Bat - family values while Jason has his own ideas of how to save the city. Eventually, they realize they need to work together to defeat the common enemy. It could show their growth and how they overcome their ideological differences.
One idea could be a friendly competition between them to see who can solve a particular mystery in Gotham first. This would showcase their detective skills.
Perhaps Jason Todd is being manipulated by a greater enemy. This enemy convinces him to kidnap Damian as part of a larger plan to disrupt the Bat - family. Jason, still dealing with his own traumas and insecurities, falls for it. He takes Damian, not fully realizing the implications of his actions. As for Damian, he would be a feisty captive, constantly trying to escape and fight back against Jason.
One idea could be a story where Nightwing has to take over Batman's duties temporarily in Gotham. He faces a new villain who is specifically targeting Batman's absence and Nightwing has to prove himself not just as a replacement, but as a hero in his own right.
One idea could be a story where Baby Nightwing is discovered by the Justice League. They have to figure out how to take care of him while also protecting him from villains who might want to use him. Another could be a time - travel story where an older hero goes back in time and meets Baby Nightwing, and has to ensure his safety so that the future doesn't change.
A great plot could be that there's a new vampire in Gotham who is creating chaos by turning innocent people into vampires. Nightwing, with his detective skills, starts to investigate. As he gets closer to the truth, he discovers that the vampire has a personal vendetta against him. It could be an old enemy who was turned into a vampire and now wants to make Nightwing's life a living hell.
One idea could be that Nightwing is captured by a powerful new villain in Gotham. Batman has to use all his detective skills to find Nightwing's location. Then, in a intense showdown, he battles the villain's minions and finally rescues Nightwing. Maybe Nightwing was being held in an abandoned warehouse on the outskirts of the city.
One idea could be a story where Batman has to carry an injured Nightwing out of a dangerous situation, like a collapsing building during a fight with a powerful villain. It could show Batman's concern and determination to save his protege.