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.
Iruka sensei could be one of the main characters. He was very important to Naruto in his childhood. In this fanfiction, Naruto going back in time might have a special interaction with Iruka. Also, characters like Jiraiya might be involved as he was Naruto's mentor and his actions in the past could be changed or influenced by Naruto's time - traveling.
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.
The other Konoha 11 members would likely be involved too. They might be split in their opinions. Some would firmly stand by Naruto, while others might be swayed by the village's reasons for denying him. Hinata, for instance, would probably be one of Naruto's biggest supporters and might even try to fight against the decision in her own way.
Hinata would be an important character as Naruto's wife. She could support Naruto in his Hokage duties and also play a role in the social aspects of the village. Their children might also be part of the story, representing the new generation.
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.
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.
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.
In this fanfiction, Naruto might go back to the time when he was a child. He could use his future skills and wisdom to outwit his enemies from that time, like Orochimaru. He could also help his friends, like Sasuke, in a different way. Maybe he could prevent Sasuke from leaving the village in the first place. This would lead to a completely different story arc for both of them and for the whole Konoha village.
Obviously, the 5th Hokage herself. Then there would probably be Naruto, as he is a central character in the Naruto universe. Sakura might also be there, as she is one of Naruto's closest friends. And Kakashi could make an appearance, given his importance in the story. Shikamaru, with his intelligence, could also be involved, perhaps as an advisor to the 5th Hokage.
Obviously, Naruto himself is central. His family like Hinata and Boruto would be very likely to be involved. Sasuke is also a key character as Naruto's friend and ally. Kakashi, being Naruto's former teacher, could also play a role. Shikamaru, as Naruto's advisor, would be important in any political or strategic situations. And then there are the other members of the Konoha 11, like Sakura who could be involved in medical support or combat situations if needed.
The other main characters could include the Hokage of that time, like Hiruzen Sarutobi. Naruto might interact with him to try and influence the decisions of the village. Also, members of the Uchiha clan such as Itachi would play significant roles as Naruto could try to change their fates as well.