Sakura could also be present. She might be observing the training and learning some things herself, or she could be helping Kakashi in some way, like providing medical support during intense training exercises.
He might learn some advanced chakra control techniques. For example, better management of his Nine - Tails chakra. Kakashi, being a skilled ninja, could teach Naruto how to blend his own chakra with the Nine - Tails' more effectively, which would enhance his combat abilities.
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.
Iruka could be included. He was Naruto's first teacher and has his own connection to Kakashi. His presence can bring out the different teaching styles between him and Kakashi. Another good character is Jiraiya. His relationship with Naruto as his godfather and his connection to Kakashi through being comrades can add some interesting storylines.
Sasuke could be a great addition. He could be a rival to Naruto even at a young age, and Kakashi would have to deal with their constant bickering. His brooding nature would add an interesting dynamic to the story.
Kakashi's training style, which is often strict and methodical, would likely make Naruto more disciplined. Naruto is usually a bit of a wild card, but under Kakashi's tutelage, he would have to follow a set routine and be more precise in his actions.
One possible plotline could be Kakashi teaching Naruto some super - advanced jutsu that Naruto then uses to surprise his friends in a sparring match. For example, Kakashi might teach Naruto a special lightning - style jutsu that Naruto masters and combines with his Rasengan.
Well, one possible plot could be that Naruto, having experienced so much growth himself, decides to pass on his unique ninja skills and values to a young Kakashi. He might teach Kakashi some of his signature jutsus like the Rasengan, but also lessons about friendship and never giving up. Naruto could also share his own experiences of dealing with loss and loneliness, which would be really interesting considering Kakashi's own past traumas.
Iruka - sensei. He was Naruto's first teacher and has a connection to Kakashi as well. He could provide some emotional support or some important backstory information that helps Naruto and Kakashi in their journey in the fanfic.
Often, Naruto is paired with Kakashi in such fanfictions. Their bond from the original series can be explored in new ways in the context of Kakashi's reincarnation. For example, Naruto might be the one to discover Kakashi's reincarnated form and help him adjust.
Kakashi, the copy ninja with his Sharingan, and Naruto, the boy with the Nine - Tails inside him. In this fanfiction, their characteristics will be explored more deeply during the timeout situation. Kakashi's calmness will contrast with Naruto's restlessness, creating interesting interactions.