One possible fanfiction could be about a Sith Lord from Star Wars ending up in the Naruto universe. Maybe he tries to use the Force to control the chakra, but finds that it's a completely different power system. He could then form an alliance with some of the villains in Naruto, like Orochimaru, who are also interested in power and dark arts.
A plot could involve a conflict where the Covenant from Halo somehow gets involved in the Clone Wars. The Clone troopers and the Jedi would have to figure out how to fight this new and strange enemy. The story could explore how the different powers and abilities in both universes interact. For example, the Force versus the Spartans' enhanced physical abilities. It could also show how the Jedi Council reacts to the arrival of these unknown warriors from another dimension.
In this crossover fanfiction, Thor's hammer could be the key to many things. It could be a powerful weapon against the Empire's technology. Maybe the Sith would try to steal it for their own purposes. The story could also explore how Thor's Asgardian nature and powers interact with the different species and cultures in Star Wars. There could be a lot of action - packed scenes where Thor uses his strength and powers to take on the Empire's forces, all while trying to figure out how to return home.
First, understand the core elements of both universes. Know Lucifer's character traits like his arrogance and his ability to manipulate. For Star Wars, understand the Force, the different factions. Then, create a unique plot. Maybe Lucifer is drawn to the dark side of the Force because it reminds him of Hell. Start with a strong hook, like Lucifer suddenly appearing in the middle of a Jedi council meeting.
In a Lucifer - Star Wars crossover, the story could take many directions. For instance, Lucifer could end up on a planet like Tatooine. He might encounter Luke Skywalker during his early days. Lucifer could either be a hindrance or an unexpected ally to Luke. His presence could also disrupt the balance of the Force in unforeseen ways. The fanfiction could explore how the Star Wars characters react to Lucifer's otherworldly presence and how he, in turn, adapts to the Star Wars setting.
One popular 'Star Wars Crossover Fanfiction' is the one where Star Wars characters cross over with the Star Trek universe. It's really interesting to see how the Jedi and the Federation crew interact. Another is the crossover with Lord of the Rings, imagining how the Force would work in Middle - earth.
A plot could center around a lost Star Wars character ending up in the Sekirei world. This character, perhaps a young Jedi in training, has to find a way back home. In the process, they befriend a Sekirei and start to understand their way of life. Meanwhile, back in the Star Wars galaxy, the Sith sense an unusual power shift due to the connection between the two worlds. They send agents to the Sekirei world to investigate and try to disrupt the harmony there. The young Jedi and their Sekirei friends must then work together to stop the Sith and also find a way to reopen the portal to send the Jedi home.
First, you need to understand the core elements of both universes. Know the characters, their motives, and the rules of their worlds. For example, in Transformers, there's the concept of Energon, and in Star Wars, the Force. Then, create a plot that combines these elements in a logical way. Maybe a Decepticon is after a Sith artifact that has the power to control both Cybertronians and Star Wars characters.
One possible plot could be that Supergirl, through some sort of inter - dimensional rift, ends up in the Star Wars universe. She might team up with the Rebel Alliance. Her superpowers would be a great asset against the Empire. For example, she could easily take down Imperial starships with her heat vision or super strength. Maybe she'd have to learn to use a lightsaber too, which would be an interesting addition to her powerset.
One great 'DC Star Wars Crossover Fanfiction' is 'The Jedi of Gotham'. It combines the dark and brooding atmosphere of Gotham with the Force - using elements of both universes really well. Another one is 'Superman in the Galaxy Far, Far Away' which has Superman dealing with the politics and battles in the Star Wars universe in an interesting way.