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.
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.
I think Archer from 'Stay Night' and Jeanne from 'Apocrypha' would be an interesting pairing. Archer is a complex character with his own set of ideals and a tragic past. Jeanne, being a Saint, has a very different set of values. Their interactions could be full of philosophical debates as well as strategic planning when facing a common enemy. Another interesting pairing could be Rin from 'Stay Night' and Sieg from 'Apocrypha'. Rin is a powerful mage and Sieg is a unique Servant. They could learn a lot from each other's magic and abilities.
One of the most interesting pairings would be Hawkeye and Sven. Hawkeye could ride on Sven while using his archery skills to fight enemies in the frozen landscapes. It would be a unique combination of mobility and ranged attacks. Another good pairing is Loki and Hans. They both have a devious side and could plot together to cause trouble in the crossover. However, the Avengers and the Frozen heroes would have to work together to stop their evil plans. And Scarlet Witch and Elsa could also be a fascinating pairing. Scarlet Witch's powers of manipulation and Elsa's ice powers could create some really cool and powerful combinations when they team up against the common enemies.
Another great combination could be Archer from Fate Stay Night and Kazuya from Freezing. Archer's cynical and experienced nature would contrast well with Kazuya's more naive and kind - hearted personality. In a battle situation, Archer's long - range archery skills combined with Kazuya's support abilities for the Pandora could create some really cool combat scenes. Plus, their different outlooks on life would lead to some interesting philosophical discussions between them.
Saber would be really interesting. Her noble and chivalrous nature would contrast with the rough - and - tumble world of Skyrim. She has a strong sense of justice and honor, which could put her at odds with some of the more morally gray characters in Skyrim. Her swordsmanship skills would be a great asset in a land full of combat, and her magical abilities could be a mystery to the mages of Skyrim. Also, her backstory as a king in her own world could lead to some really interesting interactions with the Jarls and other leaders in Skyrim.
It's really hard to say who would be the most powerful. On one hand, in Fate Stay Night, Servants like Gilgamesh have incredible power. His Gate of Babylon contains countless noble phantasms. But in the Naruto world, characters like Naruto in his Six Paths Sage Mode are also extremely powerful. He has the power of the tailed beasts and can use all kinds of powerful jutsu. However, if we consider a crossover, it might be someone who can combine the powers from both worlds. For example, if a mage from Fate could learn to use chakra and combine it with their magic, they could be very powerful. Or if Naruto could somehow gain the abilities of a Servant, like the ability to use noble phantasms, he would be unstoppable.
Harry and Elsa would be a very interesting pairing. Harry has dealt with a great burden of being 'the chosen one' and Elsa has had to bear the weight of her powers. They could understand each other's isolation and the fear of their own abilities. They could exchange stories about how they overcame their insecurities and learn from each other's experiences.
Sora and Elsa would be really interesting. Sora, with his positive and adventurous spirit, could help Elsa come out of her shell more. Elsa, with her powerful ice magic, could offer Sora a different kind of magic to understand and work with.
I think Shirou Emiya from Fate and Rin Okumura from Blue Exorcist would be an interesting pairing. Shirou is a self - taught mage who is very determined, and Rin is a powerful exorcist. They could learn a lot from each other's fighting styles and magical abilities.
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.