One way to combine them is to have Star Wars characters somehow transported to Earth during WW2. For example, a Jedi could use the Force to land on Earth and end up helping the Allied forces. Maybe they use their lightsabers to fight against the Nazis in a way that surprises everyone. The advanced technology from Star Wars could also play a role, like using a starship's scanners to detect enemy movements.
One way is to have the Star Wars characters time - travel to WW2. For example, Darth Vader could end up in a battle and his advanced technology and powers would shock the soldiers. It would be a cool scenario where the dark side of the Force meets the real - world chaos of war.
Another aspect to consider is the story arcs. Just as in Star Wars Rebels there are character developments and plot twists, in a WW2 - inspired fanfiction, these could be based on real historical events. For instance, a character could be inspired by the story of Dunkirk, where they face seemingly impossible odds but manage to survive and come back stronger, much like the Rebels in their battles against the Empire.
One interesting plot could be that the Emperor from Star Wars decides to use Earth as a testing ground for a new weapon. He sends some of his minions to Earth during WW2. The people of Earth, not understanding the true nature of these invaders, fight back. Meanwhile, a group of Jedi, who have been secretly observing Earth, decide to intervene. They train some of the bravest Earth soldiers in the ways of the Force, creating a new breed of warriors to take on the Emperor's forces. This would involve a lot of character development as the Earth soldiers learn to use the Force and adapt to this new way of fighting.
It can be depicted as a primitive planet compared to the high - tech Star Wars worlds. Maybe with simple technologies like cars and guns that seem archaic to Star Wars characters.
Often in Star Wars fanfic, Earth is used as a contrast to the more familiar Star Wars planets. Its cultures, technologies, and societies are so different from what we see in the movies and shows. For example, a fanfic might have a story where a Star Wars character is sent to Earth on a diplomatic mission and has to learn about Earth's complex political systems, which are nothing like the galactic empires and republics they're used to.
One idea could be an Earth OC who is a scientist accidentally transported to the Star Wars universe during the Clone Wars. This OC could use their scientific knowledge from Earth, like advanced medical techniques or understanding of certain technologies, to help the clones or Jedi in unexpected ways.
One creative plot is when Naruto characters are reimagined as Jedi or Sith in the Star Wars Clone Wars setting. It gives a whole new perspective on their powers. Another is having the Clone Wars' droids in the Naruto world, causing chaos with their advanced technology.
Well, you could write a fanfic where a character uses a toothbrush in an unusual way. Maybe they are in a strange world where a lemon has magical powers. The toothbrush could be the key to unlock the lemon's power, and this could be the plot of the fanfic.
The Earth soldier could fit in by being a bridge between two different worlds. They could bring Earth's values and military ethics to the Star Wars universe. They might start off as a prisoner or a stowaway on a ship, but as they interact with the characters, they start to share their knowledge. Their unique perspective could help the characters in the fanfic to see things in a different light, like how to better defend a planet or how to negotiate with different species.
Another option is to write fanfic based on the politics and power struggles within the Star Wars galaxy. You can explore how different factions vie for control, make alliances, and the consequences of their decisions.