In this fanfic, perhaps the blue lightsaber has some special connection to Naruto's chakra. It could be that the lightsaber was created by an ancient ninja who had some knowledge of a different kind of energy, similar to the Force in the Star Wars universe. Naruto then has to master both his chakra and the power of the lightsaber, and he uses it to protect his village from a new and unexpected threat that can only be defeated with the combined power of his ninja skills and the blue lightsaber.
He could find it during one of his missions. Maybe he's exploring an ancient ruin and stumbles upon the lightsaber. It could be in a chest or just lying there, and Naruto, being curious, picks it up.
A possible plot could be that Naruto is sent on a special mission to a far - off planet where lightsabers are common. There, he is given a dual bladed lightsaber by a wise old Jedi - like figure. He then has to learn the ways of the lightsaber while also dealing with local politics and power struggles. Back on Earth, his enemies sense his new power and start plotting against him. Naruto must return in time to save his village, using the skills and power he gained from his adventure with the lightsaber.
Naruto would likely become more versatile. With the blue lightsaber, he'd have a new weapon that requires different combat skills. This would force him to be more strategic in battles. For example, he'd need to learn precise strikes instead of just relying on his brute force and ninjutsu.
Well, perhaps Naruto could use the lightsaber in his ninja battles. He might combine his chakra control with the unique abilities of the lightsaber. For example, he could infuse his chakra into the lightsaber to make it more powerful or use his ninja skills to perform acrobatic maneuvers while wielding the lightsaber.
In a fanfic where Naruto has a duel bladed lightsaber, he might have to learn new combat styles. The lightsaber requires a different form of handling compared to his usual ninja weapons. He could end up training with someone who has knowledge of lightsabers, perhaps a crossover character from the Star Wars universe. This would lead to some really cool training scenes where Naruto is learning to balance his ninja abilities with the new weapon. And his opponents would be in for a big surprise when they face him with this unexpected weapon.
Maybe in the fanfic, Naruto enters an alternate dimension where the Sharingan is blue. He discovers that he has this new - found ability and must use it to find his way back home. Along the way, he meets different versions of his friends and foes, and the blue Sharingan gives him an edge in battles and also helps him understand the secrets of this strange dimension.
One way could be that Naruto discovers some ancient Jedi teachings in a hidden scroll in the Ninja world. He uses his chakra control skills, which are similar to the Force control in a way. He might shape his chakra into the form of a lightsaber blade, perhaps with a unique color based on his chakra nature, like a blue blade if his chakra has a water - like quality. Then he starts to train himself in the new - found 'lightsaber - like' combat style, combining it with his existing ninja moves.
Well, an interesting plot could involve a fusion of the energy systems in both Naruto and Dragon Ball universes. Naruto, as Super Saiyan Blue Naruto, could be tasked with saving both universes from a threat that is causing the boundaries between the two to collapse. He would have to use his newfound powers, which combine chakra and ki, to stop the chaos and restore balance.
Perhaps the Blue Eyes White Dragon is a spirit sealed within Naruto since birth, but he doesn't know about it until he reaches a certain level of power. As he discovers this, he has to face challenges not only from his enemies in the Naruto universe but also from forces that want to capture the dragon. He has to train to master the dragon's abilities, which include flight and powerful energy blasts, all while still being a ninja.
In the fanfiction, the double lightsaber might be a gift from an unknown entity. Naruto, being the curious and adventurous type, would start training with it. He'd have to learn how to handle the two blades simultaneously, which could be a whole new challenge. This could lead to new forms of combat that blend Naruto's existing fighting styles with the lightsaber techniques.