The character could have the ability to use chakra with their sword. They might be able to perform ninjutsu through the sword, like creating fire or lightning attacks. Also, they could have super - fast sword strikes similar to some of the advanced swordsmanship techniques in Naruto.
The Naruto swordsman in the fanfiction could possess the ability to channel their chakra into the sword to enhance its durability. In combat, they could use their chakra to create illusions, confusing their opponents. They might also have a unique sword - drawing technique that is extremely fast and powerful. Similar to how Zoro has his own sword - fighting style in One Piece, this Naruto swordsman could bring in a whole new set of skills. They could use their chakra to heal themselves to a certain extent as well, which would be an advantage in the dangerous world of One Piece where medical help might not always be available.
Well, it could be really interesting. The Naruto swordsman might bring unique sword - fighting styles from the Naruto world into One Piece. Maybe they'd join a pirate crew and use their skills in battles against the Marines or other pirates. Their ninja - like agility combined with swordsmanship could make them a formidable force on the Grand Line.
He could develop the ability to better withstand the different climates in One Piece. Since he's immortal, he might experiment with his body in ways others can't. Maybe he could learn to breathe underwater like a fish - man over time due to his long - lasting life.
One potential storyline is that there is a chaos - causing entity in both the Naruto and One Piece universes. Naruto, in his search for a way to stop it, ends up in the One Piece world and meets Newgate. Newgate, with his vast experience and power, joins Naruto. They then gather a group of both ninjas (from Naruto's world who also end up there) and pirates. They train together, combine their powers, and fight against this entity that wants to destroy both worlds. Along the way, there are moments of friendship, rivalry, and discovery as the two different cultures collide.
Madara could potentially be a wildcard character in One Piece fanfiction. He might not have a clear - cut allegiance. He could start off by helping a group like the Revolutionary Army, but then later switch sides depending on his own self - interests. His complex personality and powerful abilities would make him a character that could change the course of the story at any moment. He could introduce new concepts and powers to the One Piece world, and his interactions with the existing characters would be full of drama and tension.
He could have the ability to manipulate the concept of law itself. For instance, he could make it a 'law' that any attack aimed at him misses. This would be like a natural defense mechanism. Another ability could be to set laws on the use of chakra, like 'only I can use fire - style jutsu in this area' which would disrupt his opponents' combat strategies.
It could have the ability to see chakra flow in extreme detail. This would allow Naruto to detect hidden traps or enemies who are using chakra - concealment techniques. He could also use it to analyze the weaknesses in an opponent's jutsu just by looking at the chakra patterns.
Naruto could have a Zanpakuto with the ability to create illusions of hope. Given his character, it would make sense for his Zanpakuto to have an ability that gives his opponents a vision of a better future if they stop fighting. This would be a non - violent way of ending battles, which aligns with Naruto's ideology. Another possible ability could be to transform his chakra into a tangible form that can be used to either heal or boost the strength of his allies. It would be like his chakra is being channeled through the Zanpakuto in a more controlled and versatile way.
It could have super speed, allowing it to quickly dash across the battlefield and catch enemies off - guard.
With the Rinnegan, he could have abilities like the Six Paths techniques. He might be able to use the Preta Path to absorb chakra attacks. And with the Hyoton, he could create ice - based jutsu that are much more powerful than normal ice jutsu, like freezing an entire area instantly.
Naruto might gain the ability to tap into a primal energy within him due to his wrath powers. This energy could allow him to heal faster when injured in battle. Also, he could have the power to influence the emotions of his enemies. When they look into his eyes during his wrath - filled moments, they could be filled with fear or hesitation. Additionally, his physical attacks could carry a sort of 'wrath - curse' that weakens his opponents over time as they are continuously exposed to his wrath - powered strikes.