Obviously, Naruto and Kurama are going to be main characters. Since it's about Kurama going back in time, he'll be central to the story. Naruto will also be important as Kurama's jinchuriki and the one whose life Kurama is likely to impact. Minato might also be a significant character as he was Naruto's father and had a major role in the original story. And there could be appearances from other key characters like Sasuke, as Naruto's relationship with him was a big part of the original Naruto series.
Naruto and Kurama are the main characters without a doubt. But we can't forget about Hinata. In the original story, she was Naruto's love interest. If Kurama changes the past, it could also affect their relationship. Tsunade might also be a main character as she was the Hokage at one point. Her decisions and actions could be influenced by Kurama's time - traveling. And of course, villains like Orochimaru or Pain could also play important roles if Kurama tries to change the events related to them.
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.
Obviously Naruto would be one of the key characters. Since it's about his generation going back in time, he would be central to any attempts at changing the past. His knowledge and his will to protect his village would drive many of the actions.
He could meet his past self. It would be really interesting to see how he interacts with his younger, more naive self. He might try to give advice to his past self, like how to better control his power or avoid certain dangerous situations.
The main characters are likely to be Kurama and a bunch of unnamed kids at first. But as the story unfolds, we might find out more about these kids. They could be orphans with special powers that only Kurama can understand or help develop. Maybe one of the kids has a natural affinity for the nine - tailed fox's chakra. There could also be a kid who is initially very skeptical of Kurama but later becomes his biggest supporter. And of course, Kurama himself, with his vast power and complex personality, will be central to the interactions with the kids.
Gohan will most likely encounter other Z - fighters like Krillin and Tien. They were all part of the group back then. Also, there's a good chance he'll meet Master Roshi. Roshi was a key figure in Goku's training, so his interaction with Gohan could be really interesting. He might also come across Bulma, who was always involved in the Dragon Ball story, either by accident or because he needs her help with some time - related technology or something.
Naruto would be a very likely character to interact with Hinata. Since they have a strong connection in the original story, in a time - travel scenario, their relationship could develop in new and interesting ways. Maybe Hinata could be more open with her feelings earlier in time.
One interesting plot could be Kurama using his knowledge from the future to prevent certain tragedies in Naruto's past. For example, he might stop Orochimaru's early attacks on Konoha more effectively. Another plot could be Kurama helping Naruto train earlier and more efficiently, leading to Naruto becoming much stronger at a younger age. And perhaps Kurama could also change some of the relationships within the village, like improving Naruto's standing among the villagers much sooner.
Sasuke is also very popular. As Naruto's friend and rival, many fanfictions explore how their relationship would be different if Naruto had a second chance. For example, Sasuke might be more open to Naruto's friendship earlier due to Naruto's new approach influenced by his future knowledge.
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.
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.