Perhaps a time - travel fanfiction where Leia goes back in time and meets a younger Anakin Skywalker (before he becomes Darth Vader). She tries to prevent his fall to the dark side, and in the process, they form an unexpected bond. When she returns to her own time, Vader somehow remembers this connection in his subconscious and it affects their interactions.
One idea could be a story where Darth Vader discovers Leia's true identity earlier and struggles with his loyalty to the Empire and his newfound knowledge of his daughter. He could secretly protect her from the Emperor's wrath.
A plot could involve Leia being captured by Vader and instead of the typical enmity, they start to have conversations that make each of them question their beliefs. For example, Leia might see a glimmer of good in Vader, and Vader might start to doubt the Empire's ways more deeply. This could lead to a complex relationship development between them.
One idea could be that Darth Vader discovers his connection to Leia earlier and secretly tries to protect her from the Emperor's more sinister plans. He might use his position within the Empire to subtly divert threats away from her.
A plot could involve Darth Vader having visions of a different future where he and Princess Leia are on the same side. These visions start to haunt him, and he begins to subtly protect her from the Emperor's wrath. In the meantime, Leia senses a change in Vader's behavior and tries to figure out if she can use this to the advantage of the Rebel Alliance. For example, she might try to convince him to turn against the Empire completely.
A plot could involve Darth Vader having a moment of hesitation when facing Princess Leia. He sees in her a strength and spirit that reminds him of his past self. This moment of doubt could lead to a series of events where he starts to secretly help her in small ways without the Emperor knowing.
One idea could be exploring Darth Vader's identity before he became encased in the suit. Maybe he rediscovers his old self and tries to reconnect with his past relationships. Another could be him having to face the Jedi without the intimidating suit, relying solely on his raw Force abilities.
Perhaps Darth Vader's dark side powers are misinterpreted in the Naruto world as a new and extremely dangerous form of jutsu. Naruto and his friends might try to find a way to seal these powers. Meanwhile, Vader is on a quest to find a way back to his own universe, and in the process, he starts to question his own dark ways after seeing the camaraderie among the Naruto characters. He could end up having a change of heart and use his powers for good in the Naruto universe.
In some fanfiction, there could be a scenario where Leia discovers her connection to Darth Vader much earlier. Maybe she has a vision or some sort of Force - related encounter that reveals the truth. This would lead to a very different dynamic in the story as she grapples with this knowledge and how it affects her fight against the Empire. For example, she might try to reach out to the good in him, creating an internal struggle for Vader between his loyalty to the Emperor and his newfound connection to his daughter.
Well, there's a fanfiction where Darth Vader finds Luke and Leia in a Jedi temple. The temple has some sort of ancient power or secret that they are all after. Vader initially wants to use the power for the Empire but then realizes that his children's connection to the Force and the temple is something he needs to consider. There could also be a fanfiction where Vader finds them in a diplomatic setting, like a meeting between the Rebellion and the Empire. This would create a tense situation where Vader has to balance his role as a Sith Lord and his new awareness of his family.
Another plot could be set in an alternate universe where Ahsoka manages to reach out to the little bit of Anakin still left in Darth Vader. She tries to redeem him, and through a series of encounters, they start to question their own paths and the Sith vs. Jedi ideology.
One idea could be that the OC is a rebel spy who gets captured by Darth Vader. Instead of killing her immediately, he becomes intrigued by her tenacity and they start to have a series of tense conversations that gradually lead to an unexpected understanding between them.
One idea could be a story where Darth Vader secretly trains Luke in the ways of the Force before Luke fully realizes who he is. This would add an interesting layer of secrecy and moral conflict for Vader.