Darth Vader is very popular too. Some fanfiction delves into his inner conflict during the Galactic Civil War. There could be stories where he has brief moments of hesitation about his loyalty to the Emperor, or where he has secret encounters with Rebels that make him question his path of the Dark Side.
In some fanfiction, there are stories of Imperials who start to question their loyalty to the Empire during the Galactic Civil War. For example, an Imperial officer might witness the atrocities committed by his superiors and decide to defect, bringing valuable intelligence to the Rebellion. There could be a whole adventure around his escape and journey to the Rebel side.
Luke Skywalker is extremely popular in Galactic Civil War fanfic. His journey from a simple farm boy to a Jedi Knight during the war is a great source of inspiration. Boba Fett also has a lot of fans in fanfic. His mysterious nature and his role as a bounty hunter in the chaotic times of the war make him an interesting character to write about. Additionally, Wedge Antilles, as a skilled Rebel pilot, is often featured in fanfics.
One interesting concept could be the exploration of lesser - known characters' backstories during the Galactic Civil War. For example, how the ordinary soldiers on both sides of the conflict lived and what they thought. Another could be the creation of new starship designs that were used in battles but not shown in the original movies. And also, fanfics might explore the political intrigue behind the scenes that influenced the course of the war.
A young Imperial cadet who is forced to choose between loyalty to the Empire and his own moral compass during the civil war. He might end up being a key figure in the conflict.
In a Civil War vampire story, vampires could have also affected the war by changing the morale of the troops. If rumors spread about vampires in the area, soldiers would be constantly on edge. This fear could make them less effective in combat. And if some soldiers believed that vampires were on their side, it might give them a false sense of invincibility, which could lead to overconfidence and mistakes on the battlefield.
A story could focus on a powerful Sith Lord who sees the civil war as an opportunity to take over the Empire completely. He manipulates both sides of the conflict to further his own dark ambitions.