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.
Another way is through a connection with his past. Maybe he discovers something about his family, like an heirloom or a hidden message from Padmé. This rekindles his humanity and makes him want to turn away from the dark side. He then uses his skills and power to fight for the right causes, like protecting the innocent and overthrowing the Emperor.
Yes, in some fanfics, C3PO might recognise Darth Vader. C3PO is a protocol droid with a vast knowledge database. If the fanfic adheres to the basic Star Wars lore, C3PO would likely be aware of Vader's identity and his importance in the Galactic Empire. However, the nature of fanfics allows for a lot of creative liberties, so there could also be scenarios where C3PO's recognition of Vader is altered or not as straightforward due to some unique plot twists or alternate universe settings.
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.
Padmé could be a main character. Since Darth Vader is without his suit, it could be a scenario where he's reliving memories of her, and she could appear as a Force ghost or in his dreams, guiding him in some way. Another character could be Obi - Wan Kenobi. Their relationship was complex, and without the suit, Vader might be more vulnerable, and Obi - Wan could try to sway him back to the light side.
He might be shocked by the advanced technology. The Empire's weaponry would seem primitive compared to future tech. He could also be intrigued by the new forms of the Force if they had evolved.
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.