In some darth vader snaps fanfiction, he could snap and turn against the Emperor. Maybe he realizes the Emperor's true motives are not in line with his own. He then starts a secret rebellion within the Sith ranks, using his strategic skills and dark powers to undermine the Emperor's rule.
One interesting plot could be Darth Vader snapping and deciding to take on the entire Jedi Council by himself in a show of ultimate power. He might use his dark side abilities in ways not seen before, like bending the very fabric of the Force to his will.
One interesting plot could be Darth Vader traveling back in time to prevent his own fall to the dark side. He might try to change the events that led him to become Vader, like saving Padmé. Another could be Vader traveling to the future and seeing the downfall of the Sith, which makes him question his loyalty to the dark side. He could then try to find a way to change the future of the Sith order.
Well, obviously Darth Vader is the central character. But often, other characters like Luke Skywalker can be involved. Maybe Luke tries to reach out to Vader during his 'snap' moment, hoping to turn him back to the light side.
One interesting plot could be Darth Vader traveling back in time to prevent his own fall to the dark side. He might try to change the events that led him to become a Sith, like saving Padmé.
One idea could be a crossover with Star Trek. Darth Vader could find himself on the Enterprise and have to deal with the Federation's values, which are very different from the Sith's. Maybe he'd be forced to team up with Kirk and Spock to fight a common enemy.
One interesting Darth Vader OC fanfiction could be about a new character who is a force - sensitive mechanic. This character gets caught up in Vader's plans when Vader discovers their unique skills. They might end up helping Vader repair his suit in a more advanced way, leading to some unforeseen consequences and an interesting power dynamic between them.
One interesting story could be about a female character who is a rebel spy and has a fateful encounter with Darth Vader. She initially fears him but as the story progresses, she discovers a hidden side of his complex personality. This type of fanfiction often plays on the contrast between the dark and menacing Vader and the light - representing the female character.
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.
One idea could be a crossover where Darth Vader somehow ends up in the wizarding world. Maybe he's mistaken for a very powerful dark wizard and Hogwarts has to figure out how to deal with him. Another could be a story where Harry Potter discovers the Force and has to learn to use it alongside his magic. A third idea might be a scenario where Darth Vader is resurrected in the Potterverse and teams up with Voldemort, causing chaos for the Order of the Phoenix.
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.
One possible plotline could be Padme hiding her pregnancy from the Jedi Council. Another could be Darth Vader finding out about the pregnancy and struggling between his loyalty to the Sith and his love for Padme and their unborn child. Or perhaps Padme trying to find a way to raise the child away from the dark side's influence.