Well, Iruka - sensei could be a supporting character. He might check in on Naruto from time to time to see how he's doing under Kakashi. Tsunade could also play a role. Maybe she has some special tasks for Kakashi and Naruto as part of Naruto's apprenticeship. And then there are Naruto's other friends like Choji and Kiba. They could be involved in group training sessions or missions that are related to Naruto's training with Kakashi. For example, they could be the ones Naruto has to protect during a mission as a test of his skills learned from Kakashi.
Supporting characters could include the other jonin in the village. For instance, Gai could be involved. He might challenge Kakashi to a friendly spar, with Naruto observing and learning from it. Hinata could also be a supporting character. She might be secretly cheering Naruto on during his training. And the old - timers like the Third Hokage could make an appearance. He might give Kakashi some advice on how to train Naruto better or have some important mission in mind for them. Also, the Akatsuki members could be in the background as potential threats that Naruto is being trained to face as Kakashi's apprentice.
Kakashi himself would also be a central figure. His role as a mentor would be crucial. He could be shown guiding the apprentice, sharing his wisdom and his own experiences as a ninja, like his time in the ANBU or his relationship with his former teammates.
Danzo might be an antagonist. He's always been power - hungry and might see Naruto as a threat, especially if Kakashi is guiding and protecting him. Danzo could try to undermine Kakashi's efforts to raise Naruto and might even send his root agents to spy on them or cause trouble.
Sasuke could be a side character. Since Naruto is getting special training from Kakashi, Sasuke might feel jealous or motivated to train harder himself. Sakura could also be there, perhaps she tries to learn from Kakashi's training methods to help Naruto better. Another potential side character could be Iruka, who might check on Naruto's progress from time to time and offer some words of encouragement.
In this fanfiction, the plot might revolve around the relationship between Naruto and Kakashi as master and apprentice. Kakashi could be guiding Naruto not just in combat skills but also in understanding the deeper meaning of being a shinobi. They might go on special missions together where Naruto has to rely on Kakashi's wisdom and training more than his own brute strength. Also, Kakashi might share some of his own past experiences with Naruto, which would help Naruto grow both as a fighter and as a person.
Definitely Obito. Since they have a long - standing connection, it would be interesting to see how their relationship played out during Kakashi's Anbu days. Maybe Obito was still alive and had his own secret missions within the Anbu that intersected with Kakashi's.
A healer character could be added. This healer could be the one who discovers a hidden power within the apprentice that could change the course of their journey. Another potential character could be a mysterious traveler. This traveler has seen many different worlds and has knowledge that could either help or hinder the apprentice.
Another plot could revolve around Naruto's relationship with Ibiki. Ibiki might have some dark secrets from his past that he slowly reveals to Naruto as they train together. Naruto would then have to deal with these revelations and how they impact his view of Ibiki and the world around him. It could be a story of trust and growth between the two.
Sasuke could be a popular character. He might be involved in the story in a way that either helps or hinders the situation where Naruto hurts Kakashi. For example, if Sasuke tries to stop Naruto from doing something stupid that would hurt Kakashi.
Orochimaru could still be an antagonist. He might see Naruto as a threat especially if Kakashi is training him intensively. His goal of obtaining power could lead him to target Naruto.
Naruto himself could be a great crossover character. Since Kakashi is his mentor in the original series, seeing them interact when Kakashi is a kid could be really interesting. They could have a different kind of dynamic, with Naruto perhaps being the more experienced one in some aspects. Another potential character is Goku from Dragon Ball. The contrast between Kakashi's ninja skills and Goku's martial arts and superpowers would create a really exciting crossover.