Well, in this type of fanfiction, Naruto could change the relationships he had at the academy. He may befriend Sasuke earlier and in a different way, perhaps preventing Sasuke from being so cold towards him initially. Also, he could have more time to train with his classmates and help them improve too, which would make for a very different dynamic in the group.
Obviously Naruto himself would be the central character. His friends like Sasuke and Sakura would also be involved. Iruka - sensei would play an important role as Naruto's teacher at the academy again. And characters like Kakashi might also make an appearance, perhaps to give Naruto some special training or advice based on his 'second chance' at the academy.
Jiraiya is often a popular character in 'Naruto sent back in time fanfiction'. Since Naruto has a strong bond with him in the original series, in these time - travel stories, Naruto can learn even more from Jiraiya in the past and they can have new adventures together. Kakashi is also favored as he can be a mentor to Naruto in a different way with Naruto's new perspective.
One interesting plotline could be Naruto using his future knowledge to prevent the Uchiha massacre. He might be able to change things in a way that doesn't lead to Sasuke's downward spiral. Another could be him training his younger self to be stronger faster, so that he can face the early threats in the Naruto world more effectively.
One interesting plotline could be Naruto using his future knowledge to prevent certain tragedies. For example, he might stop the Uchiha massacre by warning the clan or finding a way to resolve the conflict between them and the village earlier. Another could be him training his younger self more effectively, leading to a much stronger Naruto at an earlier age. He could also change the way he interacts with characters like Sasuke, maybe preventing Sasuke from leaving the village in the first place.
Well, Hinata is often a popular character in these fanfictions. Since Naruto has a chance to redo things, his relationship with Hinata can start earlier or be developed in a more in - depth way. Jiraiya is also a favorite. Imagine Naruto going back and being able to spend more time with Jiraiya, learning even more from him. And of course, Itachi. Naruto could potentially change Itachi's fate, and fans love to explore this possibility in the fanfiction.
One possible reason could be to correct some mistakes in the future. Maybe there were some events that led to a really bad outcome, like the destruction of the Hidden Leaf Village, and Kami thought sending Naruto back in time could prevent it. Another reason might be to give Naruto a chance to learn more about his predecessors and gain new powers or knowledge that could help him in his original timeline.
In this type of fanfiction, a great plot can be Naruto going back and influencing the Third Hokage's decisions. For example, he could convince the Hokage to be more open - minded about new techniques and alliances. He might also focus on improving the living conditions in the village at an earlier stage. By doing so, he could potentially change the future of the entire Hidden Leaf Village and the shinobi world in general.
Perhaps Naruto is waiting for the right moment. He could be observing his classmates and the teachers in the academy to figure out who he can really trust. By holding back his power, he can better assess the situation and the people around him without revealing his full capabilities too soon. Also, he might not want to disrupt the normal order of the academy. Naruto might have a sense that if he goes all - out, it could cause chaos and that's not what he wants at this stage.
Obviously, Naruto himself is the main character as he is the one sent back in time. Sasuke is also often involved as Naruto's relationship with him is a central part of the Naruto story. Kakashi could be involved too, as Naruto might seek his help or try to influence his training methods. Also, the various Hokages might be important characters as Naruto could interact with them in the past to change the course of events.