Thane Krios and Darth Maul. Thane is a deadly assassin in the Mass Effect universe, and Darth Maul is a Sith assassin. It would be fascinating to see them in a battle of wits and skills. Thane's stealth and marksmanship against Darth Maul's lightsaber skills and Sith magic would make for an intense encounter.
Sakura and Liara would make an interesting pair. Sakura, with her medical ninjutsu skills, could collaborate with Liara, who is also very knowledgeable in the medical and scientific fields. They could exchange knowledge about different forms of healing and perhaps even come up with new techniques by combining their respective medical expertise.
Lara Croft and Commander Shepard would be an obvious and very interesting pairing. They are both strong leaders and adventurers. Lara's knowledge of ancient civilizations and her survival skills could complement Shepard's military leadership and combat experience in space battles. They could learn a great deal from each other.
Another plot idea is that the Mass Relay network somehow connects to hyperspace lanes in the Star Wars universe. This causes chaos as ships from both universes start popping up in each other's space. A group of Mass Effect characters and a group of Star Wars characters could come together to try and restore order and figure out how to separate the two networks again.
For me, the pairing of Miranda and Emerald could be really exciting. Miranda's genetically - enhanced abilities and her strategic mind could be a great influence on Emerald. Meanwhile, Emerald could show Miranda some of the more underhanded tactics used in RWBY's world. Also, Kaidan and Ren would be an interesting combination. Kaidan's biotic powers and Ren's ability to control his Aura could lead to some interesting experiments in combining their powers. They could also bond over their more reserved personalities.
A popular one is 'Mass Effect in the Star Wars Galaxy'. This fanfiction takes the Mass Effect crew and drops them into the Star Wars universe. It's fascinating to see how they adapt to the Force - based society. They have to deal with Sith Lords while also trying to find a way back to their own galaxy. There are a lot of plot twists and great character development.
Shepard and Captain America would be a great pairing. Both are leaders and have a strong sense of justice. Shepard could learn about Captain America's more old - fashioned values and leadership style from a different time, while Captain America could be impressed by Shepard's ability to lead in a diverse and technologically advanced universe.
Deku and Shepard would be an interesting pairing. Deku is a young hero - in - training with a lot to learn, and Shepard is an experienced leader. Shepard could mentor Deku, and Deku could show Shepard the power of having a quirk. Their different backgrounds and skills would make for great character development.
I think Thor and Chewbacca would be a really fun pairing. Thor with his god - like powers and hammer, and Chewbacca with his brute strength and loyalty. They could have some really comical moments together, like Thor trying to understand Chewbacca's growls and Chewbacca being in awe of Thor's lightning.
I think Luke Skywalker and Captain America would make an interesting pairing. Luke has his strong connection to the Force and his journey to become a Jedi, while Captain America has his unwavering sense of justice and leadership. They could learn a lot from each other's moral compasses. Another great pairing could be Darth Vader and Loki. Both are complex characters with a dark side. They could scheme together or, in an interesting turn, Vader could try to turn Loki to the light side.