It could be Ruby. Her speed semblance gives her an edge in combat, and if she were to master the Force on top of that, she would be extremely powerful. She has the determination and leadership skills that could make her a force to be reckoned with in both the RWBY and Star Wars universes combined.
I think Yang could be a strong contender. Her strength and ability to absorb and redirect energy are already formidable. In a 'rwby star wars fanfic', if she were to learn to use the Force, especially the more aggressive aspects of it like the Sith do, she could be one of the most powerful. She has a fiery personality that could drive her to great heights in both power and influence.
The most powerful character in a Star Wars Halo crossover fanfic could be different depending on the situation. If it's a battle of brute strength and combat skills, Master Chief would be up there. But when it comes to the power of the mind and manipulation, characters like Emperor Palpatine have an edge. However, if we consider the potential for growth and the ability to inspire others, a character like Leia Organa could be very powerful. She has leadership skills and is also Force - sensitive, which could be a deadly combination when combined with Halo technology or allies.
It could be Naruto. His ability to harness and control large amounts of chakra is already very powerful. If he were to also gain the ability to use the Force, he would be nearly unstoppable. He could use his Sage Mode along with the Force to sense danger from afar and attack with great force.
I think Rey and Ruby would make an interesting pairing. Rey is a powerful Force user and Ruby is a skilled Huntress. They could learn from each other's combat styles. Rey could teach Ruby about using the Force - like instincts in battle, and Ruby could show Rey how to use her Crescent Rose more effectively.
It's hard to say for sure, but Anakin Skywalker could be a strong contender. His raw power in the Force, especially before his fall to the Dark Side, was immense. If he were to face off against a Voltron Paladin, his ability to use the Force to predict attacks and his lightsaber skills would be a formidable combination. However, the Black Paladin of Voltron also has leadership and combat skills that could give Anakin a run for his money.
It's hard to say for sure, but Superman has a lot of raw power. His physical strength, speed, and durability are off the charts. However, in the Star Wars universe, the Force can be extremely powerful too. If someone like Yoda or Palpatine fully utilized the Force against Superman, it could be a very close match. But Superman's ability to fly and his heat vision give him an edge in a straight - up fight most of the time.
It's really hard to say. Superman has incredible strength, speed, and a whole bunch of other powers. But then you have characters like Darth Sidious who are extremely powerful in the Force. If they were to face off, it would depend on the situation. Maybe in a physical fight, Superman would have the upper hand, but Sidious could use the Force to manipulate and deceive. So it could go either way.
Sasuke might also be a strong contender. His Sharingan gives him an edge in combat and perception. In a Star Wars setting, he could use his Sharingan to predict his opponents' moves in lightsaber duels or even sense the presence of the Force in a unique way. And his thirst for power could drive him to master both ninjutsu and the Force quickly.
Goku would be a strong contender. His ability to reach new levels of power through Super Saiyan forms and his combat skills could make him very powerful in the Star Wars universe. He could potentially use the Force in addition to his ki.
Ultimately, it depends on how the crossover is written. If it's a story that focuses on technological superiority, then Iron Man or some of the more tech - savvy Avengers could be the most powerful. They could create new weapons or devices that give them an advantage. But if the story is more about spiritual and magical powers, then the Jedi and Sith would likely be the most powerful. For example, if the story is set in a way that the Avengers have to adapt to the rules of the Star Wars universe, then the characters who can quickly master the Force would be the most powerful.
It's hard to say for sure. Naruto has his Nine - Tails chakra mode which gives him incredible strength, speed, and the ability to heal quickly. But in the Star Wars universe, the Force - users like Yoda or Darth Sidious have amazing powers. Yoda can move large objects with his mind and has great wisdom. Darth Sidious can shoot lightning from his fingers and manipulate minds. If they were in the same world, it would depend on the situation. In a physical fight, Naruto might have an advantage, but in a battle of mental manipulation, the Sith Lords would be tough opponents.