Sasuke could also be a very powerful character in this crossover. His Sharingan abilities combined with some of the dark magic from the Harry Potter world could make him a formidable opponent. But then again, Hermione with her quick thinking and ability to master new spells could also hold her own against him. It really depends on how the crossover is set up and what abilities are allowed to be combined.
It's really hard to say. Goku has the ability to reach extremely high power levels with his Super Saiyan forms. But Naruto has the Nine - Tails' power and his own Sage Mode. If they were combined, it might be someone like Goku who has also mastered chakra. He could use the power of the Nine - Tails along with his ki, which would make him insanely powerful.
It's hard to say. Naruto has his huge chakra reserves and powerful jutsu. But Harry has the power of love and some really strong spells. However, I think Dumbledore would be very powerful in this crossover. He has great wisdom and extremely powerful magic. He could probably figure out how to use Naruto's chakra to his advantage if they were on the same side.
Perhaps Naruto combined with Toph. Naruto's agility and combat skills along with Toph's earthbending mastery would be quite a combination. Toph could sense enemies from afar using her earthbending senses and Naruto could quickly engage them in combat. Also, Naruto could use his clones to help Toph with larger - scale earthbending projects, like building massive structures for defense or offense in a battle.
Thor could also be very powerful. He has his Asgardian strength and his hammer (or Stormbreaker). If he were to also gain the ability to use magic like the wizards in Harry Potter, he could be near - invincible. He could call lightning while also casting spells. And his knowledge of different realms could give him an edge in any battles that span across the combined universes.
Honestly, it might be a combination of characters. For instance, if Batman and Hermione Granger worked together. Batman is known for his intelligence and strategic planning. Hermione is extremely intelligent and well - versed in magic. Batman could come up with a plan to take on a powerful enemy, and Hermione could use her magic to execute it. They could analyze the enemy's weaknesses, whether it's a superpower or a type of magic, and then use their combined skills to defeat them. This combination of brains and magic could make them a very powerful force in the combined fanfiction world.
Well, if we consider Harry Potter himself, he has the power of love and the ability to face great evil. But when compared to some of the Servants in 'Fate Stay Night', he might seem less powerful at first glance. But his determination and the fact that he has overcome death multiple times could give him an advantage. On the other hand, a character like Archer from 'Fate Stay Night' has a wide range of skills and the ability to analyze situations quickly. In a combined fanfiction, it would depend a lot on the situation and how the powers interact. For example, if it's a battle of wits, Dumbledore or Archer might have the upper hand, but if it's a battle of pure power, Gilgamesh or a magically enhanced Harry Potter could be the victor.
I think Harry Potter himself would be very powerful in this crossover. He has the experience of fighting dark wizards and his magic skills. If he was in the MHA world, he could use his magic to enhance his physical abilities like the characters with quirks. His ability to resist the Imperius Curse and his knowledge of defensive magic would give him an edge over many MHA villains.
It could be Akuma. He is extremely powerful in the Street Fighter universe with his dark Hadou powers. In a combined universe, his ability to manipulate dark energy could be enhanced by the magic in the Harry Potter world. He could potentially learn spells and use them in combination with his fighting skills, making him an almost unstoppable force.
However, one could also argue that Alien X from Ben 10 Omniverse, if combined with Naruto's willpower and determination, would be the most powerful. Alien X has reality - warping abilities, and Naruto's strong spirit could potentially control and direct those powers in ways that we can't even imagine in the context of the fanfiction.
There's also the idea that a character like Luigi, who is often overlooked but has his own unique skills, could become very powerful when combined with Naruto's abilities. Imagine Luigi using the invisibility power - up along with Naruto's stealth skills. He could be a formidable opponent in this fanfiction crossover.