Well, in the fanfiction, the rare sword might have some sort of special power. It could be linked to an ancient ninja clan. Naruto might have to go on a quest to discover the true nature of the sword and how to fully utilize it. This could lead to him making new allies or enemies along the way.
The sword could potentially change Naruto's fighting style completely. Since he's mainly known for his shadow clones and Rasengan, the addition of a sword could add a whole new dimension to his combat. He might start training with Kakashi or some other sword - expert ninja to master the use of this rare weapon. And who knows, this sword could also have a connection to the tailed beasts, like it was used in the past to seal or control them in some way.