I think Rin would be an interesting character to pair with Kakashi in time travel fanfictions. Since she was an important part of Kakashi's past, their relationship could be explored further. Maybe Kakashi travels back to save her from her tragic fate, and they end up having a different kind of relationship as a result.
Kakashi is often a favorite. His cool and mysterious demeanor, along with his powerful jutsu, make him a central and exciting character in fanfiction. He has a lot of room for backstory exploration.
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.
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.
There are many great writers. Some popular ones might be those who have been writing in the Naruto fanfiction community for a long time. They understand the characters' personalities well. For example, there's a writer named 'LeafFan99' who often writes stories focusing on character development, like how Sakura grows under Kakashi's tutelage.
" My Bestie Is the Zombie King " was a completed novel. After the apocalypse, the female protagonist's best friend became the Zombie King. They survived the threat of zombies and faced various challenges together. The novel was full of horror and horror elements, and it also depicted the growth and changes of the female protagonist in the apocalypse.
In the Cinderella story, her best friend could be considered the mice. They help her a great deal. For example, they make her dress when she is not allowed to go to the ball by her stepmother and stepsisters. They are always there for her, scurrying around and using their little mouse skills to get things she needs.
It could be his dog. Dogs are often considered man's best friend, and in a story about a boy, a dog would be a very likely candidate. The dog could be loyal, always by the boy's side, and they could go on all sorts of adventures together.