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.
One possibility is that there was some sort of spiritual or chakra - based connection between Naruto and Nagato. Nagato, being the possessor of the Rinnegan, recognized Naruto's strong will and the fact that he was on a path to change the ninja world for the better. Through this connection, Nagato was able to transfer the power of the Rinnegan to Naruto. It could also be related to the nature of the Sage of Six Paths' power that was somehow involved in this transfer, as both Naruto and Nagato were related to the Sage in different ways.
When Naruto gets the Rinnegan from Nagato in fanfiction, it can completely transform his role in the story. He not only gains new combat capabilities but also a new level of understanding of the ninja world. The Rinnegan might give him insights into the origin of ninjutsu or the true nature of the tailed beasts. This could lead him on a new quest to uncover secrets related to the Rinnegan and use that knowledge to reshape the ninja world. Moreover, it could also change how other villages view him. Some might see him as a potential dictator with such great power, while others might see him as the ultimate savior.
In some fanfictions, Naruto might get the Rinnegan from Nagato through a transfer of power. This could be due to Nagato seeing Naruto as a worthy successor and using some sort of jutsu to pass on the Rinnegan's power before he dies. Another possibility is that there is some sort of magical or spiritual connection between them that enables the transfer.
Well, it could mean that Naruto's view of the world and his relationships with others would change. The Rinnegan comes with a lot of knowledge and a different perspective. He might see the ninja world in a more complex way. Also, it could affect his relationships with his friends and allies. Some might be in awe of his new power, while others might be a bit wary. And in terms of the story, it could open up new plotlines, like exploring the full potential of the Rinnegan in Naruto's hands and how he uses it to face new and old enemies.
One major implication is that Naruto's power level would skyrocket. The Rinnegan is an extremely powerful dojutsu, so he would be able to use a whole new set of abilities. For example, he could use the Six Paths techniques more effectively than before.
In some fanfiction concepts, it might be due to a unique chakra interaction. Maybe the Kyuubi's powerful and ancient chakra somehow triggers a latent ability within Naruto that results in the manifestation of the Rinnegan. It could also be part of some kind of prophecy or destiny within the fan - created world of the story.
It could also be a situation where Naruto's connection to Hagoromo is deepened in the fanfiction. For instance, Naruto might have a vision or a spiritual encounter with Hagoromo. During this encounter, Hagoromo realizes that Naruto is the key to bringing true peace to the ninja world. So, he imparts the power of the Rinnegan to Naruto to help him achieve this grand goal. This would be a more complex and involved process, perhaps involving Naruto learning about Hagoromo's past and his own role in the grand scheme of things.
In some fanfictions, it could be through a strange and powerful jutsu transfer. Maybe Madara, on the verge of defeat, decides to transfer his Rinnegan power to Naruto for some unforeseen reason, like seeing a new path for the ninja world in Naruto.
He might become much more powerful. With the Rinnegan, he could gain new abilities like the Six Paths powers, which would make him a force to be reckoned with in battles.