In the fanfiction where Naruto has Sharingan in one eye, how does he obtain it?

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.

Well, in some fanfictions, he might obtain it through a strange encounter. Maybe he stumbles upon an ancient relic during a mission that contains the power of the broken eye dojutsu and it somehow bonds with him.

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 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.

Well, in some fanfictions, he might inherit it from an unknown ninja clan. Maybe his parents left it for him and it was hidden until he discovers his true heritage.

Well, he might obtain it in a fight. Maybe after defeating an enemy who had stolen Zabuza's sword from its original place. Or perhaps he discovers it in an old, forgotten hideout where Zabuza once stashed his things.

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, 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.

He might gain enhanced perception abilities, which would be a huge boost to his combat skills. With the Sharingan, he could predict his opponents' moves more accurately.

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.