In a fanfiction scenario where Naruto finds a lightsaber, he could potentially incorporate it into his fighting style. He's always been creative in combat. He might use his ninja skills like speed and agility along with the lightsaber's unique capabilities. For example, he could use his shadow clone jutsu and have his clones all wield the lightsaber in different ways to confuse his enemies.
On the positive side, it might inspire new technology in the ninja world. The unique energy and design of the lightsaber could give the ninja inventors new ideas. For example, they could try to create a similar type of weapon that uses chakra instead of the lightsaber's energy source.
In this fanfiction, Harry could potentially use the lightsaber to his advantage in battles against dark wizards. The lightsaber's unique cutting ability could be a great asset. He might also face challenges like having to keep it hidden from the Ministry of Magic which doesn't recognize non - magical weapons. And there could be a whole plot about where the lightsaber came from, like if it was brought to the wizarding world by a mysterious traveler from another dimension.
Perhaps it's given to him by a mysterious figure. This figure could be from another dimension or a very old ninja who has been in hiding for a long time. They recognize Naruto's potential and power, and decide that he is the one worthy of wielding the black lightsaber. This could be part of a bigger plan to help Naruto defeat a new and powerful enemy that neither the ninja world nor the normal means of combat can handle.
It could be a dark wizard who wants to get his hands on the lightsaber for its power. He might see it as a new tool to use in his evil plans, like using it to break into Gringotts or to fight off any who oppose him.
Naruto's fighting style would likely incorporate more acrobatic flips and spins to take advantage of the lightsaber's reach. He'd also use his shadow clone jutsu in new ways, like having clones surround an enemy while he attacks from above with the lightsaber.
Another possibility is that the black lightsaber has some sort of special power or property that ties into the Naruto universe's existing powers. For instance, it could be attuned to chakra in some way. Maybe it can be powered by chakra instead of the typical energy source in the Star Wars universe. This would create an interesting dynamic as Naruto characters would have to learn how to manage this new form of power while still using their own ninja abilities.
Sasuke could be one to help. Given their history and Sasuke's intelligence, he might contribute some knowledge about energy manipulation which could be useful for the lightsaber's power source.
If Naruto creates a lightsaber, it could be related to his connection with Kurama. Kurama's chakra is extremely powerful. It's possible that this chakra could be harnessed in a way that can mimic the energy source of a lightsaber. Naruto, being the creative and adaptable ninja he is, would then figure out how to shape and control this new form of energy into a blade, much like a lightsaber. And he would surely use it to protect his friends and the Hidden Leaf Village.
Well, in such a fanfiction, Naruto might use his chakra in a unique way to power the lightsaber. Maybe he'd combine his ninja skills with the new weapon. For example, he could use his speed to make quick slashes with the lightsaber, like his fast kunai attacks.