One interesting plotline could be Kakashi struggling to control the new power. Since the Rinnegan is extremely powerful, he might initially have a hard time adjusting. For instance, he accidentally activates its powers during a simple sparring session and causes a huge commotion. Another plotline could be how the other ninja react to Kakashi having the Rinnegan. Some might be jealous, some might be afraid, and some might see it as a new hope for the village.
Well, one way could be related to Orochimaru's experiments. Orochimaru is always into playing with genetic material and powers. He might have found a way to implant the Rinnegan - related genes into Kakashi, accidentally or on purpose. Another possibility is that in a different timeline or dimension, Kakashi is chosen by some divine force to receive the Rinnegan to fight against an ultimate evil that threatens all the ninja villages.
One interesting plot could be Naruto using the Rinnegan's powers in unique ways during battles. For example, he might combine the Rasengan with the Deva Path's ability to attract and repel, creating a new and powerful attack.
In this fanfiction, Naruto might gain incredible new powers. He could have enhanced control over all the elements and maybe even the ability to manipulate life and death like the true Rinnegan is often associated with in the Naruto lore. This would likely make him an even more formidable opponent and a great protector of the Hidden Leaf Village.
In this fanfiction, Naruto would become extremely powerful. With the Sharingan, he could gain abilities like predicting movements and copying jutsus more effectively. The Rinnegan would give him powers such as the Six Paths techniques. He might be able to use these newfound powers to better protect Konoha and face stronger enemies.
Well, he'd probably have some amazing new powers. The Rinnegan in Naruto gives the user abilities like seeing chakra and using powerful jutsu. For Harry Potter, he could use it to detect magic in new ways, perhaps even see the magical energy flowing in people. He might be able to use some sort of magic - jutsu hybrid spells. It would definitely make him even more powerful in the wizarding world.
Well, if Naruto got the Rinnegan as a kid in fanfiction, it might make him a target for various enemies and force him to grow up faster. Also, it could completely rewrite his relationships with other characters.
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 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.