The plot could start with Naruto already being the king of the White Walkers without really understanding how he got there. He then has to deal with the internal politics of the White Walker horde. Meanwhile, he discovers that there are other forces in this new world that are threatened by his new position. So, he has to balance between keeping the White Walkers in line and making peace with these other forces. Along the way, he might also try to find a way back to his own world or bring some of his friends from Naruto's world to help him in this new situation.
There could be. Fanfiction often involves unique crossovers and creative interpretations. Since Naruto has a rich world of its own and the concept of the White Walkers is also quite interesting, it's possible that some fans have been inspired to write a story where Naruto is somehow related to being the 'king of whit walkers'. However, it also depends on how many fans are into both Naruto and the idea of incorporating the White Walker concept into it.
In this fanfiction's plot, Naruto might team up with some of the local characters in the White Walker world. He could teach them some of his ninja skills in exchange for knowledge about the White Walkers. As the story progresses, Naruto discovers that there is a 'leader' among the White Walkers. He decides that to truly end the threat, he must take on this leader. He trains hard, combining his existing skills with new strategies he's learned from his new allies.
Well, in this fanfiction, Naruto might use his shadow clone jutsu to overwhelm the White Walkers. He could create a horde of clones and swarm them. Also, his Rasengan could be a powerful weapon against the undead. Just imagine Naruto spinning his Rasengan and blasting through a group of White Walkers.
It could be about Naruto discovering a hidden forest realm where he has to prove himself as the king. Maybe he has to face off against ancient forest spirits or creatures to earn that title.
Well, it could be about Naruto discovering a hidden dragon realm. He might learn to communicate with dragons and gain new powers from them. Maybe he has to fight against an evil force that wants to control the dragons for its own dark purposes.
Maybe Naruto discovers he has a hidden connection to a powerful demon king. This could lead to him having to fight against those who fear his new - found power, while also trying to control the dark forces within him.
Well, it could be about Naruto gaining the power to control the King of Hell. Maybe he makes a deal with it to save his friends. For example, he might offer his own life force in exchange for bringing Sasuke back from the brink of darkness.
One possible plot could be that Naruto is somehow transported to the world where the Soul King exists. He discovers his new role as the Soul King and has to learn the rules and powers associated with it. He might use his ninja training to face the threats that come to the Soul King's realm.
Well, it could be about Naruto achieving an even higher level of power and becoming the true 'king of kings' in the ninja world. Maybe he unites all the hidden villages under his leadership.
Well, it could be that Naruto somehow gets transported to the world where King Hassan exists. Maybe Naruto, with his ninja skills and determination, is mistaken for a great warrior like King Hassan. He could then have to take on the role and face the challenges that King Hassan would face, like protecting a certain realm or fighting powerful enemies using a combination of his ninja jutsus and the powers associated with King Hassan.