The plot of such a fanfiction might start with Naruto experiencing strange visions or dreams related to the Sage. As he investigates, he realizes his reincarnated status. Then, it could be that he has to learn to control the Sage's powers, which are far beyond what he has known before. This could lead to him having to re - evaluate his own ninja way. His friends might be initially skeptical but then come to support him. There could also be antagonists who either want to use Naruto's newfound connection to the Sage for their own evil purposes or who are afraid of the power he might gain and try to stop him from fully realizing his potential as the reincarnation of the Sage.
Naruto is surely one of the main characters since it's about his reincarnation. And there would likely be his friends like Sasuke and Sakura. Also, characters related to the Sage of Six Paths might play important roles, either as allies or antagonists.
Well, it depends on the specific fanfic. Some fanfics do portray Naruto as the reincarnation of the Sage. This concept can be used to explore different plotlines. For example, it might explain some of his unique abilities that seem to come out of nowhere in the original story. It also allows the author to create new relationships and power dynamics within the Naruto universe.
One implication is enhanced powers. He might be able to access Sage - level abilities more easily.
One interesting plot idea could be exploring how the reincarnation affects the balance of power in the Naruto world. Maybe the reincarnated character has unique abilities that disrupt the existing order among the ninja villages.
In some fanfictions, the reincarnation might lead to a different kind of bond between the main character and the tailed beasts. For example, they could communicate on a deeper level and share knowledge that was lost in the past. This could change the power dynamics in battles and how the character progresses in the story.
One possible plot could be that a powerful villain tries to create a new Buu - like being using Naruto's chakra. But instead of creating a new Buu, Naruto is reincarnated as a hybrid of himself and Buu. This would lead to a lot of internal struggle for Naruto. He would have to deal with Buu's instincts while still trying to protect his village and friends. His friends might be initially scared of him, but over time they come to understand and accept this new Naruto.
The fanfiction could have a plot where Obito's reincarnation is not a normal one. He is reincarnated with a special mission from the afterlife. He has to find a way to bring peace to the shinobi world in a different way than Naruto did. He might have to face new enemies and also deal with the old grudges that still exist among the ninja clans. His reincarnation could also bring about a change in the relationship between the different villages as he tries to use his past experiences to create a more united and peaceful ninja world.
Maybe Naruto would have some of Ichigo's powers. For example, he could have a zanpakuto instead of a kunai.
In this fanfiction, perhaps Naruto is the reincarnation of Alucard due to some ancient prophecy. His journey would then be about discovering his connection to Alucard. He could start having strange dreams about Alucard's past life and battles. As he uncovers more, he realizes he has to use Alucard's powers to save the ninja world from a new, powerful threat that only his combined Naruto and Alucard abilities can defeat.
Perhaps the story could start with Naruto having strange dreams about Goku's life. As the story progresses, he gradually unlocks Goku's powers. He could then use these powers to protect the Hidden Leaf Village in a more powerful way. For instance, when the village is under attack by a powerful enemy, Naruto could transform into a Super Saiyan - like state, shocking his enemies and allies alike. His training would also change, as he'd have to learn to control his new Saiyan powers, which would be a whole new journey for him.