One idea could be exploring Darth Vectivus's early life and how he first got involved in the dark side. Maybe he had a difficult childhood that led him down this path.
You could write a fanfiction where Darth Vectivus teams up with an unlikely ally. For example, he could form a temporary alliance with a Jedi who also has some unorthodox views. This would create a lot of interesting conflict and character development. They might start to question their own beliefs as they work together.
Another interesting concept is to write about Darth Vectivus's relationship with his Sith master. What kind of teachings did he receive? How did he eventually break free or did he? You could delve deep into the power dynamics between them and how it shaped Darth Vectivus into the Sith he became.
Perhaps an ancient evil force that Darth Vectivus accidentally awakens. This force is much more powerful than him and starts to control him, making him do things he doesn't really want to. Now Darth Vectivus has to find a way to break free from this new master while also dealing with the rest of the galaxy that sees him as the bad guy.
A cool concept would be a crossover with the Star Trek universe. Darth Vader's Sith ideology would clash with the Federation's principles. He might be intrigued by the advanced technology of the Star Trek world, and there could be an epic battle between the power of the Force and the technology of the future. Or perhaps he'd form an unlikely alliance with some of the more morally ambiguous characters in Star Trek.
Another interesting plot could involve Yoda being seduced by the dark side much earlier in his life. He then tries to recruit other Jedi to his new Sith ways, leading to internal conflicts within the Jedi Order. This could show a different side of the power dynamics and relationships in the Star Wars galaxy.
A third plot idea might be a post - redemption story for Darth Revan and Bastila. After Revan is redeemed, they both try to start a new life. But they are haunted by their past actions. The fanfiction could detail their struggles to find peace and acceptance in the galaxy, and how they deal with the people who still fear or distrust them because of their former Sith identities.
One idea could be that you insert yourself as a new apprentice to Darth Vader. You start with basic training, learning the ways of the dark side from him. Maybe you discover a hidden power within the Force that Vader is also intrigued by, and together you explore its potential.
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.
There's a fanfiction where Darth Malgus is sent on a secret mission to infiltrate a Jedi stronghold. This story is exciting as it shows his cunning and combat skills as he has to outwit the Jedi. Some fanfictions also delve into his backstory, like his family or the planet he came from. These details add depth to his character and make the story more engaging. For example, a story might reveal that he had a sister who was a Jedi, creating an internal conflict for him.
One interesting storyline could be Darth Revan being somehow resurrected during The Clone Wars and influencing the events. He might try to manipulate both the Separatists and the Republic for his own dark purposes. For example, he could use his knowledge of the Force and his strategic genius to create chaos on the battlefield, all while secretly building his own power base.
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.
One interesting story could be about Darth Vader secretly having a change of heart during the events of Star Wars Rebels. Maybe he has a brief encounter with a Rebel that makes him question his loyalty to the Empire.