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.
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 these fanfics, Nagato may help Naruto on an ideological level. Nagato once believed in a very different way of achieving peace. By sharing his journey and how he came to realize the flaws in his thinking, he can guide Naruto in his pursuit of true peace. Nagato could also use his influence over the Akatsuki remnants to prevent them from causing more chaos, which in turn helps Naruto in his mission to protect the ninja world.
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 fanfictions, Naruto and Nagato might be related through their shared experiences with the ninja world. They both faced great tragedies. Naruto could be seen as a successor to Nagato's ideals in a way. Nagato once wanted peace through force, but Naruto shows that peace can be achieved through understanding and forgiveness.
He could be more light - hearted. Instead of being burdened by his past immediately, he might start off with a more positive outlook. For instance, he could be curious about the new world around him and approach things with a sense of wonder.
Maybe Nagato had a relationship with an Uzumaki woman before he became fully involved in the Akatsuki. This woman could have given birth to Naruto but for some reason, Naruto was separated from Nagato at a young age. It could be due to the chaos and danger that Nagato was getting into with his plans for the Akatsuki.