Who would be the most interesting character pairings in a 'Fate Blue Exorcist Crossover Fanfiction'?

Weiss and Rin could be a great pair. Both are strong - willed and come from families with a certain reputation. Weiss's elegance in combat with her Glyphs and swordsmanship could be complemented by Rin's powerful magic. They might start off as rivals, constantly trying to one - up each other, but eventually realize they can achieve more by working together.

Castiel and Frank Reagan could also be an interesting pairing. Castiel with his angelic powers and Frank with his leadership and experience in the police force. Castiel might not understand all of the human politics and procedures that Frank deals with, and Frank might be initially shocked by Castiel's otherworldly nature, but they could find common ground in protecting the city from a major supernatural disaster.

I think a pairing between Shiba Tatsuya from Mahouka and Archer from Fate would be really interesting. Tatsuya is a very powerful and intelligent magician in his own right, and Archer has a wealth of combat experience and a complex personality. They could have some great philosophical debates about the nature of magic and the purpose of their powers.

One of the most interesting pairings would be Saber and Elsa. They are both strong female characters with powerful magic. Saber could teach Elsa about combat and leadership, while Elsa could show Saber how to better control her magic in a more natural way. Also, Kristoff and Lancer could be an unexpected but interesting pairing. Lancer's pride and Kristoff's down - to - earth nature would create some fun interactions.

Another great pairing could be Rin Tohsaka and the Shield Hero. Rin is a skilled mage in the Fate universe. She could help the Shield Hero understand the magic in the Fate world, and in return, the Shield Hero could show her some of his shield - based techniques that might be useful in combat. Plus, their different personalities would lead to some interesting interactions.

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.

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.

I think Harry Potter and Saber would make an interesting pairing. Harry has his own sense of justice and courage, and Saber is a noble and powerful Servant. They could learn from each other's leadership styles. Another good pairing could be Hermione and Rin. Both are intelligent and skilled in magic. They could exchange knowledge about their different magical worlds and maybe even come up with new spells or magical techniques together.