Well, a cool concept in this crossover fanfiction could be the political intrigue. In Star Wars, there's a lot of political maneuvering. In a crossover, we could see how the Voltron universe, which also has its own political structures within the various planets and species, would interact with the complex political landscape of Star Wars. The Galactic Senate could have some interesting reactions to the arrival of Voltron and its crew, and vice versa.
It's hard to say for sure, but Anakin Skywalker could be a strong contender. His raw power in the Force, especially before his fall to the Dark Side, was immense. If he were to face off against a Voltron Paladin, his ability to use the Force to predict attacks and his lightsaber skills would be a formidable combination. However, the Black Paladin of Voltron also has leadership and combat skills that could give Anakin a run for his money.
Starkiller can be a game - changer in Star Wars crossover fanfiction. He can bring his combat skills and Force knowledge to new settings. For example, if he's in a crossover with the Matrix universe, his ability to sense and manipulate the Force could be compared to Neo's ability to control the Matrix.
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.
The cultures in both universes are also ripe for exploration in the crossover. The Federation's values of equality and cooperation in Star Trek contrast with the more hierarchical and often morally ambiguous cultures in Star Wars. A story could focus on how characters from each side learn from or clash with the other's cultural norms.
The fanfiction 'Rey Meets the Avengers' is also a good one. In this story, Rey teams up with the Avengers. Her lightsaber skills are a huge asset when facing off against the villains. She has some really cool interactions with Iron Man, as they both are sort of tech - savvy in their own ways.
A great idea for an Echo x Star Wars Rebels crossover fanfiction would be that Echo has some sort of encrypted data in his cybernetic enhancements that could be crucial for the Rebels. The Rebels have to figure out a way to access it without harming Echo. This could lead to a lot of character - development moments as they get to know Echo and his past better, and Echo gets to adapt to the Rebels' way of doing things.
One great Star Wars Transformers crossover fanfiction is 'The Cybernetic Jedi'. In this story, Optimus Prime teams up with Luke Skywalker. It combines the heroism of the Jedi with the power of the Autobots in a really cool way. The battles are epic as they face off against the Decepticons and the Sith together.
A possible scenario is that Naruto's world and the Star Wars universe are somehow connected through a dimensional rift. Naruto, being godlike, is the only one who can traverse it. Once in the Star Wars universe, he is mistaken for a new type of Force - user. The Jedi Council wants to study him, while the Sith want to use his power for their own ends.
Character integration can be difficult too. The characters from 'it' have their own backstories and personalities that are very different from those in 'Star Wars'. Writers need to figure out how they would interact, for example, how would Pennywise react to a lightsaber? And how would a Jedi handle the presence of Pennywise? It requires a lot of creativity and understanding of both universes.