Yang and Tucker could also work well together. Yang is strong and confident, while Tucker has his own brand of bravado. They could get into all sorts of adventures and battles, with Yang using her brawler style and Tucker with his sword and unique abilities. Maybe they'd compete for who can take down the most enemies in a fight.
Weiss and Caboose. It might seem like an odd pairing at first, but Weiss is all about discipline and order, and Caboose, while a bit clueless at times, has a big heart. Weiss could try to train Caboose in a more formal way of combat, and Caboose could show Weiss that there's more to fighting than just strict rules. Their relationship could develop from Weiss being frustrated with Caboose to actually respecting his unique approach to things.
Weiss and Sarge would make for an odd but fascinating pair. Weiss is refined, proper, and used to a certain level of order. Sarge is loud, military - minded, and often a bit over - the - top. The clash of their personalities would be comical at first, but they could learn from each other. Weiss could teach Sarge some finesse, and Sarge could show Weiss how to be more assertive in a different kind of way.
Weiss and Carolina could be a great match. Weiss is a refined and skilled fighter with a strong sense of duty, while Carolina is a tough and no - nonsense military type. Their different backgrounds and approaches to combat could lead to some intense training sessions and a mutual respect as they realize each other's strengths.
I think Tucker from Red vs Blue and Yang from RWBY would be an interesting pairing. Tucker is known for his laid - back but confident attitude, and Yang is a strong and fearless fighter. They could bond over their combat skills and exchange stories about their respective worlds.
Ruby and Church could form an alliance. Ruby is always eager to make new friends and fight for what's right. Church, despite his snarky attitude, has a good heart deep down. They could bond over their leadership roles in their respective teams and share their knowledge about combat and strategy.
Mercy and Doc would also be a great pairing. They are both medical personnel in their respective universes. They could exchange medical knowledge, with Mercy teaching Doc about some of the more advanced medical technology in the Overwatch universe, and Doc showing Mercy some of his improvised medical techniques that he's developed in the Red vs Blue world.
Zero and Ruby would be a likely pairing. Zero is a powerful and skilled fighter, and Ruby has a lot of potential and a unique weapon. They could learn from each other's combat styles. Ruby could learn about Zero's more serious and battle - hardened approach, while Zero could be inspired by Ruby's enthusiasm and creativity in fighting.
I think Ruby and a young, adventurous Pilot would make a great pairing. Ruby's enthusiasm and eagerness to learn new things would mesh well with a Pilot's daredevil nature. They could exchange stories about their respective worlds while fighting side by side.
Ruby and Church would be really interesting. Ruby is all about being positive and leading her team, while Church is sarcastic and often a bit grumpy. Their different personalities could lead to some really funny exchanges. For example, Ruby might be excited to show Church her scythe, and Church would probably make some snarky comment about how impractical it looks but then be amazed when he sees her use it.
Kirby and Yang could also make an interesting pairing. Yang is strong and brash, while Kirby is small but mighty. Their personalities contrast but could also complement each other well. Yang could provide the brute force while Kirby could use his unique powers to support her in battles, like when she's facing a particularly tough Grimm.
Probably Carolina and Tex. Their relationship has a lot of depth and complexity in the original series, and in fanfiction, it can be explored further, especially with the 'lemon' aspect adding a more romantic or sensual angle.