Shizune. She was Tsunade's assistant and a very capable medical ninja. A fanfic could focus on her backstory, like how she became a medical ninja and her experiences during the various battles she was a part of. She could also have her own adventures away from Tsunade.
Create an entirely new character. For example, a young boy from a small village who has a natural talent for medical ninjutsu. He could travel to Konoha to study under the great medical ninjas there. Along the way, he faces discrimination because of his small - village origin but overcomes it with his skills and determination.
It could be a new character, an ice ninja named Hakuji. He has a tragic past, his family was killed by a rogue ninja group and he was left alone in the cold northern lands. He comes to Konoha seeking revenge at first but then befriends Naruto and changes his path.
It could be an original character. For instance, a young ninja from a small, unremarkable village who has a strong sense of justice and a hidden potential. This character could be inspired by Naruto's own journey, starting from being underestimated but growing into a powerful force during the war.
Kakashi could also be the main character in a different take on 'naruto rogue ninja fanfiction'. Imagine if for some reason, Kakashi was framed as a rogue ninja. He would have to use his intelligence and combat skills to clear his name while also dealing with the challenges of being an outcast. He might even discover some dark secrets about the Hidden Leaf Village in the process.
It could also be a powerful and jealous ninja from another village. This ninja is envious of Naruto's growing power and popularity. He decides to create a false narrative about Naruto being a threat to all the villages and starts a war against him. Naruto would then have to prove his innocence and stop the war before it destroys the ninja world.
Maybe an entire rival village decides to target the prodigy. They see the potential threat that the prodigy poses to their own village's dominance, so they send their best ninjas to take the prodigy down.
It could be a group of rogue ninja who have a vendetta against Naruto. They might see his new status as a rogue as an opportunity to take him down. Maybe they were once defeated by Naruto when he was in the village, and now they want revenge. Also, there could be some hidden shinobi clans within the village who oppose Naruto's new path and try to stop him for their own reasons, like protecting the village's reputation or their own power within the village.
It could be an original character. For instance, a ninja from a small, unknown village who has a unique power and is forced to participate in the war. They could be the underdog that everyone underestimates at first.
Typically, the shadow ninja themselves would be one of the main characters. They are often the focus, with their unique abilities and journey being central to the story. Another main character could be their mentor, someone who has trained them in the ways of the shadow ninja arts.
Naruto would surely be one of the main characters. He could be the one who bridges the gap between the regular ninja world and the sky ninja. Sasuke might also be involved, perhaps having some sort of rivalry with a sky ninja who has similar power levels. Sakura could play a role in healing the injured during the interactions between the two groups.
Well, Naruto would be a central character in 'naruto the reanimated ninja fanfic' as the title implies. But it might also focus on characters who are involved in his reanimation process. There could be some new characters created by the fanfic author specifically for this story who play important roles. And of course, his long - time friends and rivals from the original Naruto series, such as Shikamaru, who might be involved in dealing with the reanimated Naruto and the consequences that come with it.