It could also be related to a prophecy or a pre - determined fate in the fanfic's plot. There might be some kind of dark prophecy that says Kawaki has to kill Naruto to prevent a greater evil. Or perhaps Kawaki is being controlled by an external force that has a vendetta against Naruto and uses Kawaki as a tool to carry out the murder.
Kawaki makes his appearance in Boruto manga at a specific point, but I can't recall exactly. You might want to check the official manga sources for the precise chapter.
In this kind of fanfiction, Naruto might teach Kawaki about the values of the Hidden Leaf Village. Maybe he'd show Kawaki how to control his powers better. For example, Naruto could take Kawaki on training sessions similar to the ones he had with Jiraiya.
Kawaki might resist Naruto's teachings at first. Since he has his own way of doing things, adapting to Naruto's values and training methods could be difficult. Also, the village might not fully accept Kawaki right away, and Naruto would have to fight for Kawaki to be accepted, which is a big challenge.
In a 'kawaki kills naruto' fanfic, the story would likely take a very dark turn. The characters would be forced to reevaluate their relationships and loyalties. Sasuke, for example, would be deeply affected as Naruto was his closest friend. He might be torn between seeking revenge and trying to understand what drove Kawaki to such an act. The new generation of ninja, like Sarada and Mitsuki, would also be involved in the aftermath. They might be caught in the middle of the conflict between Boruto and Kawaki, trying to find a way to restore peace while dealing with their own feelings of loss and confusion.
One cool power often seen in such fanfiction is teleportation. This allows characters to quickly move from one place to another, escaping danger or arriving at crucial moments just in time. There are also powers related to healing, where a character has an extraordinary ability to cure any injury or illness, which can be very useful in the often - dangerous wizarding world.
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