Sasuke Uchiha has a good chance too. His Sharingan gives him unique abilities like predicting movements and copying techniques. In the merged universe, if he could also access the Force, he could become even more powerful. He has a strong will and a thirst for power, which could drive him to master both the powers of the Uchiha and the Force, making him a very dangerous adversary in the crossover fanfiction.
It could be Naruto himself. His ability to tap into the Nine - Tails' chakra gives him an incredible power boost. In the merged universe, he might be able to use the Force as well, which would make him an unstoppable force. With his speed, strength, and now potentially the power of the Force, he could easily defeat most opponents.
However, some might argue that Levi Ackerman could hold his own. His incredible speed and combat proficiency with blades could potentially make him a match for some of the Star Wars characters. If he were to get his hands on a lightsaber, he might become an even greater threat. But in the grand scheme of things, when facing the more powerful Force - using characters, he might still be at a disadvantage.
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.
Kakashi Hatake could also be in the running. His Sharingan and vast array of ninja techniques make him a formidable opponent. In the Star Wars side, Ezra Bridger has a strong connection to the Force. But Kakashi has more combat experience and a more diverse set of skills. If they were to face off, it would be an interesting battle. And of course, Naruto's ability to inspire and bring out the best in others could also be considered a form of power, which could tip the scales in his favor in this colliding universes scenario.
It's hard to say for sure, but Master Chief could be a strong contender. His combat training and advanced armor give him an edge. However, Darth Sidious is extremely powerful with his dark side abilities. He could potentially manipulate Master Chief if he got the chance. But then again, the Forerunners from Halo have such advanced technology that they might be able to counter the Force -powers. So it really depends on how the story is written.
It's hard to say for sure, but Naruto in his Sage of Six Paths mode is extremely powerful. However, Yuno from Future Diary has her own set of very deadly and unpredictable powers. If she were to target Naruto without him knowing, she could potentially be a huge threat. But Naruto also has the ability to sense danger and his large amount of chakra might give him an edge in a long - drawn - out battle.
One might argue that the Sage of Six Paths from Naruto would be the most powerful. He has the ability to create and shape the world. But in the context of a merged universe with World of Warcraft, the Lich King also has great power. He commands the undead and has powerful necromantic abilities. If they were to face off, the Sage of Six Paths' positive energy - based powers might be at odds with the Lich King's necromancy. It would be a battle of two very different but extremely powerful forces.
It could be Naruto. His ability to use chakra and his many powerful jutsu like the Rasengan and the Sage Mode would give him an edge. He also has great determination and a never - give - up attitude. He could probably adapt to the magic in the Harry Potter world quite well and use it in combination with his ninja skills.
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.
Kirito has a strong case too. He has a lot of experience in virtual reality combat and is a very skilled swordsman. In a merged universe, he could potentially learn some ninja techniques from Naruto and combine them with his own sword skills. He is also very adaptable and intelligent, which would help him face off against powerful Naruto characters. However, Naruto's raw power might still overshadow him in the end.
It could be Issei if he were to gain Naruto's abilities. He already has his own set of powerful skills in the DxD world. Adding Naruto's chakra and jutsus like the Rasengan or the ability to summon toads would make him extremely formidable.