There could be new ninja from other hidden villages that are introduced when Naruto returns. Maybe a powerful young ninja who wants to test his skills against Naruto. Or perhaps a mysterious sage - like figure who has some connection to Naruto's new power.
In the 'naruto returns powerful fanfiction', new characters can emerge from different backgrounds. For example, there could be a group of mercenary ninjas who see Naruto as a threat to their business because of his power. Another possibility is a foreign diplomat - like character who is intrigued by Naruto's return and his power and tries to form an alliance or manipulate the situation for their own village's benefit. And there could be a young trainee who idolizes Naruto and tries to follow in his footsteps, adding a new dimension to the story.
There could be a powerful mentor figure that Naruto met during his time away. This person might have taught him the secrets to his newfound strength.
There could be a hermit who takes Naruto in during his banishment. This hermit could teach him some ancient ninja techniques. Another new character might be a fellow outcast that Naruto meets, and they form a bond while living on the fringes of society.
Well, Naruto's friends and comrades from his past adventures are likely to be in it. But also, there could be some spiritual or mythical characters related to the concept of the golden fox. For example, there might be an old sage who knows the secrets of the golden fox and can guide Naruto on how to use its power properly. There could also be other villages' representatives who come to Konoha to see this 'Naruto with the golden fox' phenomenon and see if it poses a threat or an opportunity for their own villages.
The devils that oppose Rias' group could be the antagonists. They might see Naruto as an unknown threat and try to eliminate him. Also, there could be some dark magic users who don't want Naruto interfering in their plans in Rias' world.
Another potential new character could be a fellow lost soul. This character could be from another village or even another dimension. Together with Naruto, they could try to find a way out of the darkness while sharing their different experiences and knowledge.
One potential new character could be a sage who was there during Kaguya's time and has been in hiding ever since. This sage could have knowledge about the true nature of Kaguya's powers and how Naruto can control and use them properly. He might also be a bit of a trickster, making Naruto go through various trials to prove himself worthy of this knowledge.
There could be new Suna shinobi that Naruto befriends. For example, a young and talented sand ninja who has a unique jutsu related to the desert environment, like being able to manipulate sandstorms on a small scale. Another potential character could be an elder in Suna who has a lot of knowledge about the village's history and secrets, and who helps Naruto understand his new role in Suna.
There could be a Suna ninja who becomes Naruto's mentor. This ninja might have a special skill in using sand and wind chakra together and teaches Naruto how to control his own chakra better in the Suna environment. Another potential character could be a young Suna girl who befriends Naruto and shows him the ropes of living in Suna, like where to find the best oasis for water.
Maybe a foreign ninja who has a similar experience of being ostracized in their own village. They cross paths with Naruto and together they form an alliance. This foreign ninja could have unique abilities that Naruto learns from, and they both work towards changing the way they are perceived in their respective worlds.
Well, in this fanfiction, we might see some new characters related to the Nine - Tails' origin. Maybe there are other tailed beasts' hosts from a long - lost clan who come to offer their knowledge on handling such a situation. Additionally, there could be a hermit who has been observing Naruto from afar and now steps in to guide him through the difficulties of having a broken seal. And don't forget about the potential dark side characters, like a sorcerer who wants to use Naruto's broken seal to open a portal to a dark dimension.