In the fanfiction where Darth Vader travels back in time, his bond with Obi - Wan Kenobi would be full of possibilities. Imagine Vader going back to a time when he was still Anakin. He might have a newfound respect for Obi - Wan, knowing all that Obi - Wan tried to do for him in the future. Obi - Wan, for his part, could be shocked to see this changed Anakin. They could form an alliance against the emerging threat of the Sith, or Vader could try to get Obi - Wan to understand his view of the Force. Their relationship would no longer be simply that of a Jedi and his fallen apprentice, but something far more nuanced and unpredictable.
There might be a fanfiction where Obi - Wan's reaction to the destruction of the Jedi Order is explored in great detail. It could involve his efforts to save as many Jedi as possible and his feelings of guilt and determination at the same time. He might have to make some really tough decisions, and the fanfiction could show how he copes with all that.
She changes it a great deal. For starters, the gender difference can bring in a new type of relationship. Instead of the more traditional male - male rivalry, there could be an element of attraction or different kind of respect. Also, her way of handling the Force and Jedi teachings might be different, which would affect how Vader reacts to her.
One interesting idea could be a female Obi - Wan being a mentor to a younger generation in a different way than the male Obi - Wan. She might use her unique perspective to train Jedi. As for Vader, a fanfiction could explore his relationship with this female Obi - Wan in a more complex way, like they have a grudging respect for each other's skills.
One possible plot could be that Vader, without his suit, is found by Obi - Wan in a hidden location. Obi - Wan, despite their past, decides to help Vader recover. As they interact, they start to understand each other's perspectives better. Maybe they even form an uneasy alliance against a new common enemy in the galaxy.
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.
Their relationship might start with suspicion. Obi - Wan would be cautious as he's seen Vader's evil deeds. But as Vader is suitless and perhaps more 'human' in a sense, Obi - Wan could start to see the Anakin he once knew. This could lead to a slow rebuilding of trust.