Well, it could be due to a genetic anomaly that was dormant within Naruto all along. Maybe his Uzumaki and Namikaze bloodlines combined in a unique way as he faced extreme challenges in the fanfiction, which then led to the unexpected evolution of the Rinnegan. For example, if he was exposed to a strong and strange form of chakra during a battle with an extremely powerful enemy, this could be the catalyst for such a transformation.
In certain fanfiction concepts, Naruto's strong bonds and experiences play a key role in evolving the Rinnegan. His friendship with Sasuke and the experiences they've shared, like their numerous battles and reconciliations, could somehow awaken dormant powers within him. His understanding of pain and sacrifice, similar to what the original Rinnegan users might have experienced, could be the driving force. For instance, if Naruto had to make a great sacrifice to save his friends or the village, this emotional and spiritual turmoil could be what pushes his ocular abilities to evolve into the Rinnegan.
Well, in certain 'Naruto can evolve' fanfictions, Naruto's evolution could be related to his mental state. He might grow to have a deeper understanding of the ninja world and his role in it. This could lead to him evolving his combat strategies, like using his talk - no - jutsu in more creative and impactful ways during battles, rather than just relying on brute force. And he could also gain new forms of chakra control that are more refined and powerful.
In some fanfictions, Naruto might awaken the Rinnegan through a powerful jutsu overload. For example, if he combines a super - charged Rasengan with some ancient and forbidden chakra - based techniques. This could potentially trigger a genetic or chakra - system shift that results in the awakening of the Rinnegan.
It might be related to a connection with some powerful entity in the Wave arc. For example, if there's a secret shinobi from the past whose power is tied to the Rinnegan and Naruto somehow forms a bond with that power source, it could lead to the awakening. Also, the intense emotions and challenges he faces in the Wave arc might be a catalyst, pushing his chakra to a new level and awakening the Rinnegan.
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.
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.
Naruto's fighting style in fanfiction evolves in multiple ways. His physical strength and speed increase over time. He may develop new ways to combine his different powers, such as using his Sage Mode and Nine - Tails chakra simultaneously. His mental growth also plays a role. He becomes more confident and less impulsive in battle, which allows him to plan his attacks more carefully. Additionally, he might be exposed to different fighting cultures or techniques in fan - created stories, which he then adapts into his own style, making it more versatile and unpredictable.
Perhaps he could obtain the Rinnegan through some sort of ancient ritual or a gift from a powerful entity. And to become Hokage, he would need to prove himself worthy through his deeds and leadership skills, like protecting the village from a major threat.
If Naruto gains the Rinnegan in fanfiction, it could change the story in many ways. For one, his power level would skyrocket. He might be able to use all the abilities associated with the Rinnegan like the Six Paths techniques. This would make him an even more formidable opponent against enemies. Also, it could change his relationships. His friends might view him differently, either with more awe or perhaps some fear due to his new, extremely powerful ability.
In some fanfiction concepts, the chakra of the Kyuubi is not just pure fox chakra but also contains remnants of the Sage of Six Paths' power. Since the Rinnegan is related to the Sage of Six Paths, when Naruto reaches a certain level of power and harmony with the Kyuubi, the dormant Rinnegan - like power within the Kyuubi's chakra awakens in Naruto. This could be a result of Naruto's strong will and his journey to master the Kyuubi's power which eventually leads to him obtaining the Rinnegan.