A combination of Zoro and Sasuke could be very strong. Zoro's three - sword style combined with Sasuke's Sharingan and his various fire - based jutsus would give them an edge in battles. Zoro could use the Sharingan to predict his opponents' moves better while Sasuke could learn from Zoro's swordsmanship skills to improve his own combat abilities.
If Luffy and Naruto combined their powers, they would be extremely powerful. Luffy's rubber body and his Gear techniques along with Naruto's Nine - Tails chakra would make them a force to be reckoned with. They could take on any enemy easily, whether it's a powerful ninja or a fearsome pirate.
Sasuke merged with Zoro could also be very strong. Sasuke's Sharingan and his various ninjutsu like the Chidori, combined with Zoro's three - sword style and his great swordsmanship skills. The Sharingan could help Zoro predict his opponents' moves even better and Sasuke could use Zoro's physical strength to enhance his own attacks.
A character like Kaido with a quirk that made his already tough body even more indestructible would be a nightmare to face. On the other hand, Deku with the ability to use all the One Piece Haki types in addition to his multiple quirks would be an absolute powerhouse. He could use Armament Haki to strengthen his punches even more, Observation Haki to predict his opponents' moves better, and Conqueror's Haki to intimidate his foes. In a fanfiction world, the possibilities for creating the most powerful character are endless.
One interesting crossover could be the characters from Naruto using their ninja skills in the world of One Piece. For example, Naruto's shadow clone jutsu could be used in battles against pirates. Another could be the Devil Fruits in One Piece being coveted by the ninja in Naruto's world. Maybe a character like Luffy teams up with Naruto to fight a common enemy that threatens both their worlds.
Probably a combination of All Might and Gol D. Roger. All Might has incredible strength and the symbol of peace status. Roger was the Pirate King with great leadership and combat skills. Together, they would be almost unbeatable, having the best of both the hero and pirate worlds in terms of power and influence.
Sasuke with a quirk could also be extremely powerful. If he had a quirk like Shoto Todoroki's ice and fire ability on top of his Sharingan and Rinnegan, he would be a force to be reckoned with. He could use his ice to freeze opponents from a distance, then use his fire to create powerful explosions, all while using his Sharingan to predict their moves and his Rinnegan for more advanced techniques.
It's really hard to say. Luffy has his Gear Fourth form and the ability to stretch his body in incredible ways. But Naruto in his Sage of Six Paths mode is extremely powerful too. He has access to a vast amount of chakra and can use some of the most powerful jutsu. However, if we consider Kaido from One Piece, with his near - indestructible body, he would also be a top contender. So it could be any of them depending on how the crossover is written.
It's hard to say for sure. Luffy has the power of the Gum - Gum Fruit and his Haki, which gives him great strength and the ability to sense and overpower opponents. However, Naruto has the Nine - Tails' chakra and Sage Mode. In a crossover, if they were to fight, it might depend on the situation. But if we consider all - round power, Naruto's ability to create multiple clones and use a variety of jutsu might give him an edge over Luffy in some scenarios.
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.
Obviously, Naruto would be one of the main characters. He is the driving force behind the idea of rebuilding Uzushio. There might also be some Uzushio descendants who play important roles. For example, a young ninja who has a deep knowledge of Uzushio's history and traditions.
It's really hard to say. Luffy has his rubber powers and Haki which can be extremely powerful. But Naruto has the Nine - Tailed Fox and his vast array of jutsu. If they combined their powers, they would be a force to be reckoned with. However, if we consider villains, someone like Madara Uchiha with his Sharingan and all his skills, if he got his hands on a Devil Fruit, he could be extremely dangerous. But then again, Kaido from One Piece is also super tough. So, it's a tough call.