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.
One implication is that he becomes much more powerful. The Rinnegan gives him access to powerful abilities like the Six Paths techniques, which would change the power dynamics in battles in the fanfiction. He could now face stronger enemies more easily.
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.
One potential antagonist could be Orochimaru. He is always after powerful jutsus and the power of the Rinnegan would be extremely appealing to him. He might try to either steal Naruto's newly awakened Rinnegan or prevent Naruto from fully mastering it so that he can be the most powerful one in the ninja world.
In some fanfictions, Naruto might awaken his Rinnegan through a powerful and ancient jutsu. For example, he could come across a hidden scroll that contains the knowledge and power to unlock this dojutsu. Maybe a mysterious sage or an old shinobi reveals the secret to him, guiding him through a series of trials that eventually lead to the awakening of the Rinnegan.
In such a fanfiction, Naruto might gain incredible new powers. He could potentially use the Rinnegan's abilities like the Six Paths techniques. This would likely change the power dynamics in the Naruto universe completely, making him an even more formidable opponent against enemies.
One possible interesting plot could be Naruto discovers a hidden ancient scroll that details the secrets of awakening the Rinnegan. He then embarks on a dangerous journey filled with various trials and battles against powerful enemies who also want the power of the Rinnegan for themselves.
It could be a new character who is jealous of Naruto's newfound power of the Rinnegan. Maybe someone who has been in the shadows all along and now sees Naruto as a threat to their plans for world domination.
In one possibility, Naruto could be in a life - or - death battle against an extremely powerful enemy. This intense situation could trigger some latent power within him, leading to the awakening of the Rinnegan. Maybe he has a connection to an ancient power or a special bloodline that was previously unknown, which surfaces during this crucial moment.
In some fanfictions, it could be due to a powerful emotional shock. Maybe seeing a friend in great danger at Wave, like Sasuke almost dying, could trigger an unexpected connection to the Sharingan. Since Naruto has a strong bond with Sasuke, this extreme situation might force his latent Uchiha - like powers (in the context of the fanfic) to surface, awakening the Sharingan.
It could be a new character, a rogue ninja from a long - lost clan. This antagonist might have a vendetta against Naruto because they see his potential to awaken the Rinnegan as a threat to their own plans for power. They could be trying to stop Naruto from achieving this new level of power so that they can carry out their evil deeds unopposed.