Well, perhaps Darth Vader would recognize R2 from his past with Anakin. He might initially be hostile but then start to have memories resurface. This could lead to an internal conflict within Vader as he battles between his current Sith self and the remnants of his former self that had a connection to R2.
One possibility is that Vader tries to use R2 to gain an advantage over the Rebellion. He might think that R2 has valuable information about their plans. But R2 being the resourceful droid it is, could outwit Vader and escape, or even plant false information in Vader's mind if it has the right hacking capabilities.
One interesting scenario is that R2 uses its charm, if you can call it that for a droid, to make Vader question his loyalty to the Emperor. Since R2 was so close to Anakin, it could show Vader a side of himself that he has long forgotten, and this could make him start to doubt the Sith path he's on.
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.
Well, in such a fanfiction, R2D2 could use his beeps and whistles to communicate something unexpected to Darth Vader. It could be some long - forgotten information about Anakin Skywalker that makes Vader question his path. And Vader might find himself hesitating to harm the little droid because of this new - found knowledge.
One plot idea could be that R2D2 is captured by Darth Vader. But instead of destroying the little droid, Vader becomes curious about the information it might hold. He tries to hack into R2D2's memory, leading to a series of tense moments as R2D2 tries to protect the secrets within. Maybe R2D2 has some long - lost Jedi knowledge that Vader thinks could help him overthrow the Emperor.
Their relationship could start off as adversarial. Darth Vader sees R2D2 as just another piece of Rebel technology to be destroyed. But as the story progresses, he might start to respect R2D2's tenacity and the fact that it has survived so many battles. For example, if R2D2 helps Vader in some small way, like leading him out of a dangerous situation, Vader might start to view the droid differently.
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.
I really like the fanfic 'Darth Vader: The Hidden Years'. This one delves into the time period between Episode III and IV, when Vader was still adjusting to his new life as a Sith. It gives a lot of backstory and character development that you don't get in the movies. It shows how he's dealing with his new powers and his relationship with the Emperor.
A good 'Star Wars Darth Vader Fanfic' should have a deep understanding of the character. For example, it should explore Vader's duality - his past as Anakin and his current state as Vader. Also, it should fit well within the Star Wars universe in terms of the lore and the technology.
A great 'Star Wars Darth Vader Fanfic' has to have a deep understanding of the character. Darth Vader is complex, so it should show his conflict between the light and dark side. For example, fanfics that explore his memories of Padmé are often good.
One great fanfic could be 'The Redemption of Vader and the Ascent of Luke'. It delves deep into the relationship between the two. It shows how Luke's unwavering belief in the good in Vader starts to chip away at Vader's dark side. It's filled with intense lightsaber battles and emotional dialogues that really capture the essence of their connection in the Star Wars universe.