Kanan Jarrus is another good choice. As a Jedi, he has the skills to face Vader, at least to some extent. Their interactions could explore the differences between the Jedi way and the Sith way. And Kanan's relationship with his crew could also play into the story, as he tries to protect them from Vader's wrath.
Hera Syndulla could also be paired with Vader in fanfiction. Although she's not a Force - user, her leadership skills and her determination to fight the Empire could lead to some interesting scenarios. Maybe she manages to outwit Vader in a battle of wits, or she has to rescue one of her comrades from Vader's clutches.
Ezra Bridger would be a great character to pair with Darth Vader. Their interactions could be really intense, as Ezra is a powerful young Jedi in the Rebels series and Vader has a history with the Jedi. It could lead to some great battles and also some interesting moments of understanding or misunderstanding between them.
Hera could also be an interesting character to pair with Ezra. She could act as a mentor figure in a fanfiction, guiding Ezra through some tough decisions regarding the Rebellion. Their relationship could be explored more deeply, especially in terms of Ezra learning from Hera's leadership skills.
In a fanfiction, Darth Vader might finally face his past with Ahsoka. Maybe he would have moments of hesitation in their battles, as memories of their time as master and apprentice resurface. This could lead to an internal struggle within Vader, torn between the Dark Side and his former self.
One interesting story could be about Darth Vader secretly having a change of heart during the events of Star Wars Rebels. Maybe he has a brief encounter with a Rebel that makes him question his loyalty to the Empire.
One interesting fanfiction could be about Darth Vader secretly having a moment of hesitation when facing a Rebel who reminds him of his past self. Maybe he lets the Rebel escape without the Emperor knowing. It adds a new layer of complexity to his character.
Ezra's reaction would also depend on his state of mind at the time. If he was feeling confident and strong in the Force, he might be more bold in his approach to Vader. He could try to engage in a battle of wills through the Force, trying to push back against Vader's dark side influence. But if he was already weakened or doubting himself, the sight of Vader could make him feel hopeless and desperate, leading to a more erratic or panicked reaction.
Well, it's likely that there are bounty hunters. Since Vader often has need of their skills for certain tasks. They would be characters who are in it for the money but also fear Vader. And then there are the stormtroopers. They are a constant presence, following Vader's commands and being part of his military operations.
Obviously, Darth Vader is the main character. There might also be Emperor Palpatine as he was Vader's master. And we could see some Imperial officers like Grand Moff Tarkin who interacted with Vader.
In fanfiction about Ezra and Darth Vader, their interactions could also be more psychological. Vader could try to tempt Ezra to the dark side. He might offer Ezra power, saying that with his potential, he could become a great Sith. Ezra, on the other hand, could resist and try to turn Vader back to the light, using his own experiences and the teachings of the Jedi he has learned. This back - and - forth of wills could create a really engaging and complex story line.
One great 'Star Wars Darth Vader Fanfic' is 'Vader's Redemption'. It shows a different side of Vader, exploring his inner conflict in a very engaging way.