Well, it could be a really wild story. Harry's magic might interact in strange ways with Darth Vader's Force powers. Maybe Harry would try to use his spells to resist Vader's dark side influence.
The story might start with Harry being somehow transported to Vader's universe. He'd be shocked by the new environment, but his quick thinking would help him adapt. Then he'd cross paths with Vader, and the adventure would begin.
Well, one possibility is that Ahsoka tries to redeem Vader. She might see a glimmer of Anakin still in him and strive to bring him back to the light side. It would be a very emotional encounter, full of memories of their past as master and apprentice.
If Ahsoka joins Vader in fanfiction, their relationship would become extremely complex. At first, it would likely be filled with anger and resentment from both sides. Vader might see her as a reminder of his past failure as Anakin, and Ahsoka would see him as the fallen Anakin she once knew.
If it was a fanfiction like that, it would completely distort the perception of Harry Potter. Harry is a symbol of hope and light in his own universe, but if he was like Darth Vader, he'd be seen as a much darker and more menacing figure. As for Darth Vader, his iconic status as a Sith Lord might be diluted if his traits were randomly imposed on Harry Potter. It would be a very odd mash - up.
Darth Vader could encounter advanced droids that have developed personalities and even some form of Force - like abilities in this future. These droids might be a new challenge for him as they are not like the droids he is used to dealing with in his own time. He may also meet future versions of his former allies or enemies, who have been reincarnated or cloned in some strange new way, with different personalities but still with a connection to their past selves.
In the 'naruto is like darth vader fanfiction', their journey of self - discovery could be seen as similar. Naruto has to constantly figure out his place in the ninja world and how to control his power. Darth Vader is on a journey of self - discovery too, as he grapples with his identity as Anakin Skywalker and his role as Darth Vader. They also have a sense of isolation in some ways. Naruto often feels alone in his struggles, and Darth Vader is isolated in his dark armor, cut off from his former self and many human connections.
Darth Vader could meet advanced droids that have personalities and abilities far beyond what he's used to. These droids might see him as a relic from a bygone era. He could also meet future scientists who are intrigued by his cybernetic enhancements and try to study him. Additionally, there's a chance he meets descendants of his former allies or enemies, which would create a complex web of relationships and interactions.
In fanfiction, we can also see how an OC might change the power balance between Vader and Sidious. If the OC is a powerful ally to Vader, it could lead to a split in the Sith order. Or if the OC is a double - agent working for both, it can create a complex web of lies and deceptions that make for a very engaging read.