One way could be through a chakra transfer. Suppose an Uchiha with the Golden Sharingan is on the verge of death and decides to transfer their power to Naruto. This could be due to Naruto's heroic nature and the Uchiha's belief that Naruto can use the power for good. Another possibility is that Naruto accidentally stumbles upon a hidden scroll or artifact that imbues him with the Golden Sharingan when he touches it or tries to decipher it.
In fanfiction, Naruto could obtain the Golden Sharingan through a powerful ninja ritual. Maybe a sage or an ancient ninja figure passes on the power to him as a last resort to save the ninja world from a great evil. For example, if there's a threat that only the combined powers of the Uzumaki and Uchiha clans can defeat.
In fanfiction, Naruto could get the Sharingan through a blood - related connection that is revealed later. For example, it could be discovered that he has some distant Uchiha ancestry that gets activated somehow. Maybe a powerful enemy's attack awakens this dormant Uchiha blood in him, and as a result, he develops the Sharingan. It could also be that a powerful sage or a new character uses their own unique powers to bestow the Sharingan upon Naruto for a specific purpose.
In a fanfiction, Naruto might obtain the Rinnegan and Sharingan through a unique encounter. For example, he could stumble upon a dying Uchiha who transfers his Sharingan to Naruto in a moment of desperation. As for the Rinnegan, it could be related to his connection with the Sage of Six Paths. Perhaps the Sage's spirit, seeing the great need in the ninja world, bestows the Rinnegan upon Naruto. It could also be a result of some sort of genetic experimentation gone wrong but in a way that gives him these powerful eyes instead of harming him.
In fanfiction, it could be due to a strange encounter with a magical or ancient artifact. This artifact has the power to transfer the Sharingan's essence from Madara to Naruto. It might be a relic from an ancient battle between the Uchiha and some other powerful force, and when Naruto and Madara come into contact with it, the transfer occurs.
Perhaps in the fanfiction, there is a forbidden scroll that Naruto stumbles upon during the Chunin Exams. This scroll contains a secret technique that allows for the transfer of the Sharingan. Naruto, being the curious and fearless character he is, tries it out and ends up with the Sharingan. Another possibility is that there is a spirit or a deity that decides to bestow the Sharingan upon Naruto for some greater purpose that is related to the events of the Chunin Exams.
In some fanfictions, it could be through a special jutsu or ritual. Maybe Itachi, before his death, transferred his Sharingan to Naruto in a unique way, perhaps using a forbidden technique that was known only to a few in the Uchiha clan.
In some fan theories, it could be due to a unique chakra interaction. Maybe the Kyuubi's powerful chakra somehow mutates Naruto's own ocular abilities and triggers the emergence of the Sharingan. But this is just a wild fanfiction idea.
He could obtain it through a unique chakra infusion. Maybe during a battle with a powerful enemy who has some connection to an ancient chakra source, Naruto is accidentally exposed to a golden - hued chakra that fuses with his own and transforms his eyes into the Golden Rinnegan.
There could be. Fanfiction often takes creative liberties. Since Naruto is known for his own abilities and the Sharingan is a significant power in the series, a story where Naruto has a golden Sharingan could be an interesting twist. It might explore new plotlines, power dynamics, and character relationships. Check websites like FanFiction.net or Archive of Our Own to look for it.
One implication could be enhanced power. The Sharingan already has powerful abilities like seeing chakra flow and predicting movements. A golden Sharingan might have even more advanced or unique powers. Maybe Naruto could use it to see into the future more accurately or manipulate chakra in a completely new way.
One possibility could be through a forbidden jutsu experiment gone wrong. Maybe some rogue ninja was trying to create a super - powered being and Naruto ended up being the subject. The Sharingan was transplanted into him, but only one eye was successful.