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.
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.
One idea could be a what - if scenario where Anakin in his pre - Vader state somehow gets a glimpse of his future as Vader. He could then fight against the dark side within himself that would turn him into Vader. Another could be a time - travel plot where Vader is sent back to face Anakin, and Anakin has to decide whether to accept his possible future or fight against it.
A fan fiction could also explore a parallel universe where Anakin and Darth Vader are two separate entities that co - exist. They are forced to fight not because of Anakin's fall, but due to some external force that wants to see the two most powerful Sith - like beings battle it out. This could lead to an exploration of their different fighting styles and the power dynamics between them.
One of the most fascinating things is seeing Sidious's manipulation tactics in more detail. Fanfics often show the intricacies of how he plays different factions against each other. His relationship with Vader is also a rich area. Some fanfics might explore what Sidious really thought of Vader, was he just a tool or did he have some deeper feelings? And then there's the aspect of his connection to the dark side. Fanfics can take us deeper into his understanding and use of the dark side's power.
I really like 'Darth Sidious: Unveiled'. In this fanfic, we get to see Sidious from a different perspective, exploring his inner thoughts and motives more in - depth. It's fascinating to see how his thirst for power shaped his actions. Also, 'Sidious in the Shadows' is good as it focuses on his shadowy influence over different events in the Star Wars universe. There's also 'The Sidious Chronicles' which chronicles his rise to ultimate power.
One key element is the power struggle. It's about showing how Sidious' immense power in the Dark Side of the Force clashes with Maul's own strength and determination. Another element could be the backstory, like how their relationship developed over time.
In most cases, Sidious would likely win. Sidious is extremely powerful in the Force and highly skilled in combat. He has been shown to manipulate events and people on a large scale. Maul, while a formidable opponent, is not as powerful or as devious as Sidious.
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.