One common theme is the clash of motives. Mercenaries are usually in it for money or personal gain, while the Star Wars characters often have grander ideals like freedom or the balance of the Force. Another theme is the power struggle. Mercenaries may try to gain power within the existing power structures of the Star Wars universe.
Some 'Star Wars meets Mercenaries' fanfictions focus on the character development of the mercenaries. For example, a story could be about a young and idealistic mercenary who starts off working for the wrong side in the Star Wars galaxy but gradually realizes the true nature of the conflict and switches allegiances. This type of fanfiction gives a fresh perspective on the Star Wars lore from an outsider's point of view.
One interesting concept could be the combination of the different technologies. For example, the warp drive from Star Trek and the hyperdrive from Star Wars. It would be fascinating to see how they interact and if they could be used together in some way. Another concept might be the meeting of the different species. The Vulcans from Star Trek and the Wookiees from Star Wars could have some very unique interactions. They have such different cultures and ways of life that it would create a lot of interesting storylines.
In such a fanfiction, perhaps the Jedi could encounter alien species from UFOs. They might team up to fight a common enemy, like the Sith who are trying to harness the advanced technology of the UFOs for evil purposes.
Well, in such a fanfiction, we might see Darth Vader facing off against Voldemort. Vader's dark side powers and his imposing presence could be a match for Voldemort's dark magic. And perhaps Luke Skywalker could befriend Harry and help him in his fight against the Death Eaters. The Millenium Falcon could also fly over Hogwarts, which would be an amazing sight.
Well, in a Stargate meets Star Wars crossover fanfiction, we might see the characters interact in interesting ways. For example, the SG - 1 team could meet up with Luke Skywalker. They could exchange knowledge about their different forms of combat and technology. The Goa'uld sarcophagus technology might be something the Sith would be interested in, while the Jedi could perhaps learn about the Ancients from the Stargate universe. There would be a clash of different cultures and power systems, which would make for a great story.
One possible plot could be that a group of Star Wars characters, like the Jedi, encounter a UFO while on a mission in outer space. The UFO could be from a highly advanced alien civilization that has technology different from the Force - based technology in Star Wars. Maybe the aliens are looking for a new planet to colonize and the Jedi have to decide whether to help them or protect the planets in the Star Wars galaxy.
The plot could involve Jedi knights using their lightsabers in a medieval setting. Maybe they'd be part of a feudal system, with the Force being seen as a kind of magic. The Sith could be the dark lords trying to take over kingdoms.
Well, in a Frozen meets Star Wars fanfiction, we might see Olaf as a droid. He could be reprogrammed by BB - 8 to have some cool new functions. And what if the Dark Side influenced Hans? He could become a Sith - like character, causing chaos in both the Frozen world and the Star Wars galaxy. Princess Leia could also visit Arendelle and help Elsa understand her powers better, sharing her own experiences of leadership and using her abilities for the good of the people.
In a fanfiction where Rey meets Anakin, one possibility is that Anakin would see Rey as a symbol of hope for the future of the Jedi. He might take it upon himself to train her in the ways of the Force more deeply, sharing his own experiences both good and bad. Maybe he would guide her in how to avoid the dark side's temptations that he himself succumbed to.