One possible reason could be that Kakashi later realizes Naruto's potential. He might see how much Naruto has grown on his own despite being ditched, and feels guilty for not being there to guide him more. Another reason could be that Kakashi starts to understand the importance of Naruto in the overall story or the team's dynamic. Maybe he misses the bond they could have had if he hadn't ditched Naruto.
Well, perhaps Kakashi regrets it because he discovers that Naruto was facing a lot of hardships alone. In the fanfiction, Naruto might have been in situations where Kakashi's skills and experience could have made a huge difference. Kakashi could have also realized that by ditching Naruto, he unknowingly pushed Naruto towards some dangerous paths or made it harder for him to achieve his goals. Also, he may have seen how Naruto's positive attitude remained despite being ditched, and he feels bad for not being a part of that journey earlier.
Kakashi might regret ditching Naruto in the fanfiction because he finally comprehends the impact of his actions on Naruto's emotional state. Naruto is a character who thrives on positive relationships and support. By ditching him, Kakashi may have caused Naruto to feel unwanted or unworthy. Moreover, as the story progresses in the fanfiction, Kakashi could see how Naruto's strength and character are being shaped by his isolation, and he wishes he could have been there to influence Naruto in a more positive way. He may also realize that Naruto had a lot to offer in terms of friendship and loyalty, and by ditching him, he lost out on that valuable connection.
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.
One reason could be the realisation of the strong bond they could have had. Kushina might understand in the fanfiction that Naruto has been through so much alone, and she missed out on being there for him. She may regret not being able to protect him from the hardships and bullying he faced as a child.
Another reason might be related to the events that unfold after the rejection. For example, Naruto might go on to do extraordinary things and form closer bonds with other characters. Sakura could feel left out or jealous, which then leads to her regret. Also, she might have some self - realization about her own feelings at the time of rejection, thinking that she was influenced by wrong factors like social status or her own naivete.
One reason could be Kakashi's Sharingan. It's a very powerful and somewhat spooky ability. Naruto might see it in action in a way that scares him. Maybe Kakashi uses it to subdue an enemy in a really intense way that makes Naruto realize how dangerous Kakashi can be.
One possible reason could be training. Maybe Kakashi's training methods are too harsh for Naruto. Naruto is eager to become stronger quickly, but Kakashi might be holding him back in Naruto's eyes. For example, Kakashi could be making Naruto do repetitive basic drills instead of teaching him more advanced jutsu right away.
Kakashi could be in a difficult situation where he has to make a choice between Naruto and another more pressing obligation. For example, he might be under orders from higher - ups in the village to focus on training a different group of ninjas. So, even though he may like Naruto, he has to reject him in order to fulfill his other duties.
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.