The scariest might be the story of the phantom carriage that is said to race through the streets of Bristol Boro on stormy nights. It's described as a black carriage pulled by skeletal horses, and it disappears into thin air. The sound of its wheels and the neighing of the horses send shivers down people's spines.
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.
There's a story in Bristol Boro about the old school building. At midnight, some say you can hear the laughter and chatter of children who used to study there. Legend has it that there was a tragic accident in the school many years ago, and the children's spirits remain. Some witnesses have even reported seeing faint apparitions running through the hallways.
One common theme is friendship. Writers often explore how Himawari and Kawaki, who come from different backgrounds, form a bond of friendship. Another theme is growth. They both grow as characters, learning from each other.
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.
One common theme is growth. Both Himawari and Kawaki are often depicted as growing both as individuals and in their relationship. Another theme is acceptance. Since they come from different backgrounds, fanfictions usually show how they accept each other's differences.
One great 'kawaki naruto fanfic' could be one where Kawaki has to learn a new jutsu from Naruto. In many fanfics, Kawaki is often portrayed as a complex character trying to fit into the Hidden Leaf Village. He might struggle with his past and Naruto could be the one to guide him through it.
In such a fanfiction, perhaps Kawaki is driven by some extreme ideology. Maybe he believes Naruto's way of peace is a weakness and decides to take him out to change the ninja world in a more radical way.