Perhaps it's a unique staff. A staff could have different uses, like being a conduit for chakra. It could also have hidden compartments or be made from a rare material that gives Naruto an edge in battles. For example, it might be made from a metal that can absorb chakra attacks and then redirect them.
One possible plot could be that Naruto discovers an ancient technology in a hidden cave. Maybe it's a powerful weapon that was used in a long - forgotten war. He then has to figure out how to use it without it falling into the wrong hands. He might seek help from his friends like Sasuke or Sakura to understand the technology better.
Well, it could be a sword with the power to cut through any jutsu. Maybe it has some special markings that only Naruto can understand. It might also be a staff that can control the elements in a unique way, giving Naruto an edge in battles.
With his mentor figures like Kakashi, they would likely try to guide Naruto on how to handle this new discovery. They would caution him about the potential dangers and help him understand the responsibilities that come with possessing such an ancient weapon.
He could face a lot of challenges. People might try to steal the ancient weapon from him. His friends might be worried about the power it holds and try to convince him to get rid of it. But Naruto being Naruto, he would want to keep it to protect the village.
If the weapon is a chakra - enhancing tool, it will boost Naruto's existing jutsu. For example, his Rasengan could become more powerful, being able to break through stronger defenses.
In a Naruto finds ancient technology fanfiction, his relationship with his sensei, like Kakashi, could be affected in an interesting way. Kakashi would be both proud of Naruto for the discovery but also cautious. He would guide Naruto in understanding the technology. This would create a new dynamic in their relationship, with Naruto relying more on Kakashi's wisdom and Kakashi having more faith in Naruto's judgment as he deals with this new and powerful discovery.
Well, it could be a key to unlocking new powers for Naruto. Maybe it has some special chakra - enhancing properties that help him in battles against stronger foes.
It might be a set of shuriken, but not the ordinary ones. These shuriken could be larger and have a unique shape, like the outline of a wave. They could also be made of a special metal that's resistant to most forms of damage and has the ability to return to Naruto's hand like a boomerang.
His friends might be a bit wary of the sentient weapon at first. Sasuke, for instance, might be suspicious and think it could be a danger. But Naruto would try to convince them that it's okay. Over time, if the weapon proves useful, they could come to accept it.