Well, Minato could be one of the characters. He was Naruto's father and died when Naruto was just a baby. Reviving him would allow Naruto to finally have a proper father - son relationship. Another possibility is Neji. His death was quite tragic during the war, and his revival could bring some interesting plot developments in the fanfic, especially in terms of his relationship with Hinata and the rest of the Konoha 11.
One character that might be revived is Obito. His story was full of twists and turns. Reviving him could lead to a redemption arc where he could make up for his past mistakes. Also, the Akatsuki members like Deidara might be revived. His unique abilities could add more action and chaos to the fanfic's plot if he were brought back to life.
It could also be Makarov. As the guild master, he has a sense of responsibility towards all his guild members. He might have some secret magic or knowledge that could be used to revive Gajeel in a moment of great need for the guild.
In some fanfictions, Naruto might use some super powerful jutsu he created or mastered. Maybe it's a new form of Sage Mode that can reverse time on a small scale. Another possibility is that he found some ancient forbidden technique hidden in the Uzumaki clan's secrets.
Well, in the fanfic, the revival might lead to new alliances and rivalries. Suppose Obito is revived. His past actions might make some people still distrust him, while others might see his revival as a chance for him to make amends. This could create new political and social dynamics. Also, the revived characters could bring back old secrets or knowledge that had been lost. This might be a good thing in some ways, like finding a new way to fight a common enemy, but it could also be dangerous if that knowledge falls into the wrong hands.
Emotionally, Naruto would have to deal with a whole new set of family relationships. He grew up without his parents, and now having them back would be a huge adjustment. He might struggle to fit into a 'normal' family dynamic, and there could be some friction as they all get to know each other again.
Well, obviously Naruto himself would be the main character. There could also be his friends like Sasuke and Sakura, who might be involved in the interactions between the two Narutos. Maybe they are confused at first by seeing two Narutos, but then they help them figure out what's going on.
It could still be Naruto himself. Since he's the central character in the original series, many fanfics would likely continue to build on his story.
Sasuke would likely be one of the main characters to interact with Naruto. Given their complex relationship, Sasuke might be either supportive or skeptical of Naruto's newfound power. Sakura could also be involved, perhaps trying to heal Naruto if the dark power has negative effects on him. Kakashi would surely step in as well, using his wisdom to guide Naruto and make sure he doesn't lose himself in the darkness.
Naruto is a likely candidate. Given his importance in the series, a plot where he is brainwashed can create a huge impact. His powerful chakra and his role as the main character mean that if he is brainwashed, it can change the entire dynamic of the story. The enemy could use his strength against his own friends and village.
Obviously, Naruto himself would be the main character. Since it's about him growing tails, he's at the center of it all. The Nine - Tails would also play a crucial role. It's the source of his tail growth. And his friends like Sasuke and Sakura are likely to be important too. They'll probably be involved in Naruto's journey and how he deals with his new situation.
Naruto is the obvious one. His connection to the Uzumaki clan makes him the driving force behind the rebuilding. Hinata would also be likely involved, as Naruto's wife, she would support him and might contribute to the new Uzushiogakure in areas like family support and community building.