Yes, there are some. You can start by checking out fanfiction websites like FanFiction.net or Archive of Our Own. Just search for'starkiller x darth phobos' on their platforms, and you might find some interesting stories written by fans.
In many'starkiller x darth phobos fanfiction', loyalty and betrayal are often explored. Since they are both complex characters, their loyalties might be tested. They could start out as allies but then face situations where one betrays the other. Also, the theme of the Force and how it affects their relationship can be common. Whether they use the Force together in harmony or against each other can add depth to the story. And of course, the theme of love or a deep connection that defies the norms of the Sith and Jedi ways might also be present, as it often is in fanfictions to add an extra layer of intrigue to the relationship.
Starkiller in fanfiction, not the 'lemon' kind, is usually portrayed as a character with great potential in the Force. He might be shown as being in a struggle against the Sith or trying to find his own path. His relationships with other Star Wars characters like Vader or Luke are often explored, showing his place in the Star Wars universe.
Starkiller is the central character in this story. He's likely to be a character with unique abilities and a significant role in the Star Wars universe.
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.
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.
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.
A more detailed fanfiction could involve Starkiller being lost in time and ending up in Ahsoka's era. At first, they are suspicious of each other, but as they learn about the common threats they face, they start to trust and rely on one another. They could exchange knowledge about the Force, with Starkiller showing Ahsoka some of the unique combat techniques he learned from Vader, and Ahsoka teaching him about the more traditional Jedi ways. This would lead to a deepening of their characters and a great story arc as they work together to protect the galaxy from a looming danger that neither could face alone.
A fanfiction could also explore the idea of Starkiller and Ahsoka meeting in a post - Empire world. Starkiller, having broken free from his Sith past, and Ahsoka, who has seen so much of the galaxy's turmoil, could join forces to help rebuild and protect the newly - emerging peaceful systems. They would have to overcome their differences, as Starkiller has a more aggressive style while Ahsoka is more in tune with the Jedi's peaceful ways. But their shared goal of a better galaxy could bring them together. They could start by training a new generation of Force - sensitive beings, combining their unique teachings to create a more balanced approach to the Force.