One possible reason could be that Kakashi believes Naruto's sword holds some special power or secret that is crucial for a mission or for the safety of the village. Maybe he has discovered some threat that only the sword can counter, and he needs it in Naruto's possession.
Perhaps there is some prophecy or ancient lore associated with the sword. Kakashi, being well - versed in the history and secrets of the ninja world, has learned about this. He demands the sword from Naruto either to protect it from falling into the wrong hands or to use it to fulfill the prophecy. For example, the sword might be the key to unlocking a great power that could save the ninja world from an impending doom, but it needs to be in the hands of someone more experienced like Kakashi at that moment.
Naruto could also be angry. He has always been a bit hot - headed. He might think that Kakashi doesn't trust him enough with the sword or that Kakashi is trying to undermine his progress as a ninja. So, he would likely challenge Kakashi, either verbally or by showing his determination not to give up the sword without a good reason.
One possible reason could be that Kakashi is preoccupied with other important matters in the village. Maybe he has some top - secret missions or tasks assigned by the Hokage that demand his full attention, leaving him with little time to focus on Naruto.
One possible reason could be that Naruto might feel Kakashi is too strict with his training. Maybe Kakashi's methods are too harsh for Naruto, making him frustrated and gradually developing dislike.
One possible reason could be Kakashi's reputation as a strict and powerful teacher. Naruto might be in awe of his skills and fear making mistakes in front of him.
One possible reason could be that Naruto might be trying to prove his independence. He has grown and wants to show that he can handle things on his own without always relying on Kakashi's guidance.
One possible reason could be that Kakashi might be haunted by his past experiences. He has lost many comrades, and perhaps he's afraid that getting too close to Naruto and training him would put Naruto in danger as well. He might think that Naruto, being the Jinchuriki of the Nine - Tails, already has a target on his back, and training him would only make that target bigger.
One possible reason could be that Kakashi might think Naruto is not ready yet. Maybe Naruto hasn't mastered some basic skills that are prerequisites for the more advanced training Kakashi has in mind. Another reason could be that Kakashi is worried about Naruto's recklessness. Naruto has a tendency to rush into things without thinking, and Kakashi might fear that this could lead to Naruto getting seriously injured during the training.
One possible reason could be that in the fanfiction, Kakashi might have made a decision during a mission that Naruto strongly disagreed with. For example, Kakashi could have chosen to sacrifice something important to Naruto in order to achieve the overall mission objective.
It could also be due to a misunderstanding. Kakashi might be keeping some secrets from Naruto, like information about his parents or some hidden power within him. Naruto, being curious and eager for answers, could misinterpret Kakashi's motives for secrecy as a sign of distrust or dislike, which then turns into hatred.
It could be due to a misunderstanding. Kakashi might think that Naruto is getting involved with something dangerous or has some potential that he can't handle. So, in his warped way of thinking, he abandons Naruto to protect him from himself or from some unknown danger.