Another idea is to cross him over with a fantasy world. Picture Galen Marek in a medieval - like setting, using his Force powers in a world of magic and knights. He could be a mysterious figure, perhaps mistaken for a powerful wizard at first, and have to adapt to this new world's rules and challenges.
One idea could be a crossover with the Star Wars universe at a different time period. Galen Marek could interact with new characters or be part of a different Jedi order. For example, he could be sent on a mission to a planet not yet explored in the original storylines.
Arya Stark from 'Game of Thrones' could also work. It would be a very different kind of crossover. Arya's skills as an assassin could be compared to Galen Marek's combat abilities. They could find themselves in a situation where they need to rely on each other's skills in a strange new world that combines elements of both their universes.
A really interesting plot could be set in an alternate universe where Galen Marek never turned to the dark side. He and Ahsoka meet during a mission to save a planet from a natural disaster. They find out that there are dark forces trying to take advantage of the chaos. Together, they have to fight off these forces while also trying to save the planet and its inhabitants. Galen's knowledge of the Force in a more positive light and Ahsoka's wisdom as a former Jedi Padawan combine to make a great team.
One interesting fanfic could be about Galen Marek's early training. It might explore his relationship with his master in more depth than the official story. For example, how he overcame difficulties during training.
Character development is key. Since it's a crossover, seeing how Galen Marek's character adapts to a new and different universe. For example, if he's in a more technologically advanced setting, how does he use his Force powers in conjunction with new technology.
One popular Galen Marek crossover fanfiction is 'Galen Marek in the Star Wars: The Old Republic' universe. It explores how his unique Force abilities would interact with the different factions and storylines in that game's setting.
One idea could be a story where Galen Marek and Ahsoka Tano team up to face a new threat in the galaxy. They could combine their unique skills, Galen's powerful Force abilities and Ahsoka's combat and strategic knowledge. Maybe they meet on a neutral planet and at first are distrustful of each other, but as they face challenges together, they start to respect and rely on one another.
They might start off warily. Galen, being used to the ways of the Sith, would be cautious around Ahsoka, a Jedi. Ahsoka, on the other hand, would be on guard but also curious about Galen. Eventually, they could start to exchange combat techniques and stories of their past experiences.
Well, Galen Marek in a Star Wars Rebels fanfic might be a bit of an anachronism at first glance. But if you think about it, the Star Wars universe is vast. He could have been in hiding for years. In the context of Rebels, he could be a force for change. He might be drawn to the Rebellion's cause because of his own experiences with the Empire's cruelty. His presence could also attract unwanted attention from the Empire, leading to some tense moments in the fanfic. For example, the Inquisitors might sense his power and start hunting him, which could then put the Rebels in danger as they try to protect him.
One idea could be that Galen Marek and Ahsoka Tano team up to face a new Sith threat. They might initially be suspicious of each other due to their different backgrounds. Galen with his training under Vader and Ahsoka's Jedi training. But as they work together, they start to respect each other's skills and form a strong bond.
Darth Vader also makes appearances in many Galen Marek Clone Wars fanfictions. Given his connection to Galen Marek as his former master, it's interesting to see how their relationship is portrayed in fan - created stories. Writers often delve into the power dynamics and the emotional turmoil between them.