Well, obviously the two main characters are Batman from the normal DC universe and Flashpoint Batman. Batman is the well - known Dark Knight, a symbol of justice in Gotham. Flashpoint Batman is from an alternate timeline, with different experiences and a potentially different personality.
In the Injustice 2 Batman ending story, Batman manages to defeat Superman. He restores order to a world that has been torn apart by the chaos of the Injustice regime. With Superman out of the way, Batman is able to start rebuilding society, bringing back justice and the rule of law. He also has to deal with the remaining super - villains and ensure that they are locked away safely.
The 'Flashpoint Batman Graphic Novel' often has a darker and more gritty take on the Batman character. It shows a different version of Gotham City, with altered relationships and storylines compared to the traditional Batman comics.
In the 'batman flashpoint graphic novel', Batman is a major character. He has a dark and brooding presence, dealing with a world that is not as he knew it. Flash is crucial as he is the one who causes the shift to this alternate reality. Additionally, characters like Aquaman and Wonder Woman play important parts. Aquaman is involved in the conflicts between different factions, and Wonder Woman has her own motives and actions that are integral to the plot of this alternate - reality - based graphic novel.
Another plot development could be that Flashpoint Batman tries to convince the regular Batman to change his ways. He might see the regular Batman's methods as too soft or ineffective. This could create a lot of internal conflict for the regular Batman as he questions his own beliefs and methods in the face of this alternate - self's criticism.
Well, it could be about Batman trying to stop the Flashpoint Joker from causing chaos in Gotham. Maybe the Joker has a new and devious plan that only Batman can foil.
Nightwing is a great choice. He has a strong connection to Batman as his former sidekick. In an Injustice fanfiction, Nightwing could be the voice of reason when Batman starts to go too far in his fight against Superman. Their relationship, with all its history and baggage, can add a lot of depth to the story.