Naruto is the central character in 'naruto goes to the past fanfic'. His younger self is also a main part of the story. Then there are the village elders. They would be important as Naruto might try to influence their decisions. Also, the Akatsuki members in their earlier forms could be part of the story. Naruto could try to prevent some of them from going down the wrong path, which would change the whole Akatsuki's future and the ninja world's balance.
The main character is Naruto. In the past, he will surely encounter his parents. Minato and Kushina would be important characters in this fanfic. Also, Jiraiya, his mentor, would be a key figure. Since Naruto is going to the past, he might seek Jiraiya's guidance even more. And characters like Orochimaru would also be part of the story as Naruto may try to stop Orochimaru's evil plans earlier.
Obviously Naruto himself. Since he is the one going to the past, he would be the central character. His younger self would also be important as he would interact with his future self.
Obviously, Naruto and Orochimaru are the main characters. Naruto is the protagonist who is going to Orochimaru, and Orochimaru is the one Naruto is going to see.
Obviously, Koyuki herself would be a main character to interact with Naruto. She might show him around her place, introduce him to her people. Also, any of her loyal guards or advisors could interact with Naruto. They could be initially suspicious of him but then grow to trust him as they see his good intentions.
Well, Naruto is a given. Then there could be other minor gods or spirits in Kami's realm that Naruto meets. Maybe there's a guardian spirit of the ninja world that only appears when someone tries to reach Kami. Also, characters like Kakashi could be involved. He might have some knowledge about Kami that he imparts to Naruto before the journey, or he could even end up joining Naruto on his adventure to Kami.
Obviously Naruto would be one of the main characters. And from the Nova Corps, likely some of their leaders or important members like Rhomann Dey.
It could be an evil version of Sasuke. In the original story, Sasuke had his dark moments, and in a very dark fanfic, he could be fully consumed by evil and oppose Naruto in a much more malevolent way.
The main characters might interact with historical superheroes or villains that no longer exist in their present time. For instance, they could meet an ancient sorcerer - villain who was sealed away long ago. Dealing with such a character would test their skills and force them to think outside the box in terms of combat and strategy.
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.
Obviously Naruto would be one of the main characters. There might also be some original characters created for the Western setting, like a Western - style mentor for Naruto or a local hero who teams up with him.