Well, in a fanfiction scenario, Naruto could get the Sharingan by having a blood - related connection to an Uchiha that is revealed later. Maybe his mother had some hidden Uchiha heritage. For the Rinnegan, it could be due to his journey to understand the true nature of chakra. He might discover a new form of chakra that is linked to the Rinnegan and, through intense meditation and training, awakens it within himself. Or perhaps he meets a mysterious figure who imparts the power of the Rinnegan upon him as a means to save the ninja world from an impending doom.
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 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 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 fanfiction concepts, there could be a spiritual or mental connection established between Naruto and Nagato. Since Naruto has this unique ability to understand and connect with people on a deep level. Through this connection, Nagato might pass on the power of the Rinnegan to Naruto. It could be like a transfer of not just the physical power but also the knowledge and understanding that comes with the Rinnegan.
In fanfiction, the idea of Naruto having the Sharingan and Rinnegan is often a creative and out - of - the - box concept. It could be due to some kind of powerful jutsu or a unique plot device. Maybe a powerful enemy uses a forbidden jutsu that somehow transfers the powers to Naruto. Another possibility is that in an alternate universe created by the fanfic writer, the rules of chakra and kekkei genkai are different, allowing Naruto to possess these powers.
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 powerful curse. For instance, a long - forgotten enemy places a curse on Naruto that not only gives him the blue Rinnegan but also sets him on a path to either destroy the world or save it depending on how he uses the power.
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.
It could be that in the fanfiction, Naruto is exposed to a special type of chakra or energy source. This energy source could be related to an ancient artifact or a long - lost power. As Naruto has always been at the center of extraordinary events, his encounter with this special chakra could be the catalyst for him to obtain the True Rinnegan. It might also be that his previous battles and experiences have slowly been building up to this moment, and this final push of some external or internal factor causes the True Rinnegan to emerge.
One possible fanfiction could be about a character who has the unique ability to combine the powers of the Sharingan, Rinnegan, and Byakugan. For example, this character might be a long - lost descendant of powerful ninja clans. They could use the Sharingan's precognitive abilities to anticipate an enemy's moves, the Rinnegan's power over life and death in battles, and the Byakugan's long - range vision to scout out the battlefield. This would make them an extremely formidable foe in the Naruto universe.