In such a fanfiction, one possibility is that Anakin Skywalker might initially be in shock upon seeing Darth Vader. He could struggle to come to terms with what he has become. Maybe there would be a battle of wills as Anakin tries to fight against the dark side within Vader.
Luke Skywalker could be another key character. Since he is Vader's son, his presence could add an interesting dynamic. He might be the one who somehow triggers the battle between Anakin and Vader, or he could be in a position to influence the outcome of their fight, perhaps by appealing to the remaining good in Anakin or by facing off against Vader himself in a three - way struggle.
In a 'Ahsoka meets Darth Vader' fanfiction, there could be an intense battle. Ahsoka, with her Jedi skills, would be a formidable opponent to Vader. Maybe she tries to redeem him, recalling the Anakin she once knew. Or perhaps Vader sees her as a threat to the Empire and attempts to eliminate her quickly.
Well, in fanfiction, when Darth Vader meets Yoda, it could lead to a battle of ideologies. Vader, having turned to the dark side, represents power and control through the Sith ways. Yoda stands for the Jedi's connection with the Force in a more harmonious and selfless way. They could engage in a Force - powered duel where Vader tries to overpower Yoda with his dark side strength, but Yoda uses his wisdom and experience to counter.
Well, a possible storyline is that Rey is lost in a strange part of the galaxy and ends up in a place where Vader still rules. She has to use her wits and the Force to survive and deal with Vader. Maybe she tries to understand his pain and the reasons he turned to the dark side, and in the process, she changes his view a bit. Or perhaps Vader tries to turn Rey to the dark side, seeing her as a powerful addition to his ranks. There are also storylines where they are brought together by a greater power, like an ancient Force - related entity that wants them to either fight or cooperate for some grand purpose.
It really depends on how you write it. If it's Anakin at his peak before turning to the dark side, he has a lot of raw power and potential. But Vader has years of experience as a Sith Lord. So, it could go either way.
It could explore their relationship by showing the contrast between their current selves. Ahsoka is a free - thinking Jedi - like figure, while Vader is a servant of the Emperor. Their relationship could be one of enmity, with Ahsoka seeing Vader as a fallen hero and Vader seeing her as a nuisance to the Empire.
Perhaps Vader would start with 'You cannot stop me, old one.' Yoda would then calmly say 'Not so, young Skywalker. The Force is with me.' This shows the contrast between Vader's arrogance in the dark side and Yoda's confidence in the light side of the Force. There could also be a moment where Vader asks Yoda why he should return to the light, and Yoda gives a long speech about the true nature of the Force and how the dark side is a path to self - destruction.
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.