A possible plot could be centered around a new threat in Gotham. Batman and Nightwing both have different plans to deal with it. Batman's plan is more secretive and involves a lot of solo work, while Nightwing wants to involve the public and work as a team. Their conflicting plans cause them to oppose each other.
Another plot could involve a difference in ideology. Batman might believe in a more strict and unforgiving approach to crime - fighting, while Nightwing has a more lenient and rehabilitative view. This could lead to a clash between them, both physically and in terms of their beliefs.
One idea could be a misunderstanding. Maybe a villain manipulates information to make Batman think Nightwing has turned bad. So, Batman starts to hunt Nightwing, while Nightwing is confused and has to prove his innocence.
A plot idea could be that Nightwing is injured while saving a group of hostages. Batman then has to deal with the criminals who were holding the hostages as well as take care of Nightwing. The story could explore Batman's feelings of guilt for not being there in time to prevent Nightwing's injury.
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 that Batman discovers a hidden agenda within the Justice League that he believes endangers the world, so he decides to oppose them. For example, he might find out that a new technology the League is using has unforeseen and dangerous side effects.
One idea could be a misunderstanding. Maybe some false information makes Batman think Wonder Woman has been compromised and he has to stop her. Another could be a competition for a powerful, mysterious artifact that they both believe they should safeguard. And a third idea could be a mind - control situation where Wonder Woman is being controlled by an enemy and Batman has to fight her to break the control.
A great plot could involve Nightwing training a new generation of heroes in the 'Batman Beyond' universe. He could share his old - school combat techniques with the more tech - reliant heroes, leading to some interesting clashes and growth. For example, he might have a hard time getting used to the new gadgets while the younger heroes struggle with his more hands - on combat style. And together they have to face a villain who is exploiting their differences.
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.
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.
In this fanfiction, often there's a power struggle. Nightwing, with his own set of skills and experiences independent from Batman, might oppose Batman on certain principles. Maybe it's about different approaches to crime - fighting. Nightwing could be more lenient while Batman is strict.
The relationship between Batman and Nightwing is key. Their different personalities - Batman's brooding and Nightwing's more upbeat nature - create a great dynamic. Also, the action in Gotham, like taking on classic villains together, can be really exciting.
One idea could be that Robin discovers a dark secret about Batman's past that makes him question their relationship, leading to a tense confrontation. For example, if Robin finds out that Batman once made a deal with a villain that had far - reaching consequences. Another plot could involve a new villain manipulating Robin into believing Batman is a threat to Gotham, causing them to fight. Maybe the villain uses mind - control technology.