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.
It could be Naruto. His ability to use chakra and his vast array of jutsus are very powerful. In the Fate universe, he might be able to combine his chakra with the magic there. For example, he could infuse his Rasengan with magical energy, making it even more destructive.
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.
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.
It's hard to say for sure, but Naruto at his strongest form, like in his Six Paths Sage Mode, would be extremely powerful. He has incredible speed, strength, and the ability to use all kinds of ninjutsu. In the Fate world, he could give a tough fight to many Servants. However, some of the really powerful Servants like Gilgamesh with his vast collection of powerful weapons and his god - like status would also be a strong contender.
Sesshomaru could also be a very powerful character in this crossover. He has his own powerful sword, Bakusaiga, and his inhuman strength and speed. He is very experienced in combat against demons. Compared to Naruto's friends like Sakura, Sesshomaru would likely be much more powerful in terms of raw strength and combat ability. But Sakura has her own medical ninjutsu and superhuman strength when she releases her inner power, which could also be useful in different situations.
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.
Well, Erza is a very strong character in Fairy Tail. She has a vast array of armors and combat skills. However, in a crossover, Sasuke could be a real contender for the most powerful. His Sharingan gives him amazing abilities like predicting moves and copying techniques. And his Rinnegan in later arcs makes him even more formidable. But then again, characters like Gildarts from Fairy Tail are also extremely powerful with their unique magic. So it really depends on how the crossover is written and what abilities are emphasized.
It's likely that Naruto himself would be one of the most powerful. His ability to use chakra and his various jutsu like the Rasengan would give him an edge in combat. He also has the Nine - Tails' power which could be a game - changer.
Saber is often a popular choice. Her noble and powerful image makes her adaptable to many different crossover scenarios. Archer is also a favorite. His cool and mysterious demeanor can add a lot of intrigue in crossovers. And Rin Tohsaka, with her intelligence and magical abilities, can easily be incorporated into various crossovers, like a crossover with a scientific - based universe where she uses her smarts to figure out new things.