I'm not sure specifically as there could be many different interpretations in this fanfiction. But generally, it might involve Naruto having some sort of connection or power related to the 'king of the dead'. It could be about him exploring a new realm of the dead, facing challenges there, and perhaps using this new - found power to deal with enemies or protect his village.
In this fanfiction idea, Naruto being the Silent King of the Dead could bring a whole new dimension to the Naruto universe. He might possess powers over the dead, which could be used for various purposes like protecting the Hidden Villages in a different way. Maybe he could communicate with the souls of the past Hokages for advice and wisdom.
Naruto is surely a main character. Additionally, there might be some original characters created specifically for this fanfiction. For example, there could be a powerful spirit or a guide in the world of the dead who helps Naruto understand his new powers. And characters like Kakashi could also be involved, perhaps providing advice or assistance to Naruto as he deals with the implications of being the king of the dead.
He could have the ability to raise the dead shinobi to fight for him. This would give him a huge advantage in battles. For instance, he could bring back the likes of Minato or Jiraiya to assist him in crucial fights.
It varies from one fanfiction to another. Some fanfictions might depict Naruto as dead to introduce a new set of challenges for the remaining characters. For example, if Naruto dies, Konoha might be left vulnerable, and characters like Sasuke or Sakura would have to step up in different ways. But there are also plenty of fanfictions where Naruto remains alive and continues his journey, perhaps facing new and even more dangerous threats than in the original series.
Kakashi could be another important character. As a mentor figure, he might be guiding the younger generation through the difficult times after Naruto's death, using his experience and wisdom to keep the village stable.
Naruto's experience in dealing with tough opponents in his own world would help him in the zombie - filled Highschool of the Dead. He would be able to quickly analyze the situation, figure out the weaknesses of the zombies, and come up with effective plans. His friendship - first approach might also lead to some interesting relationships with the other characters in this new and dangerous world.
In this Naruto - Dead Rising fanfiction, Naruto could team up with some of the survivors in the Dead Rising world. They would be initially skeptical of his strange powers but soon realize his value. Naruto could teach them some of his ninja training techniques to help them better defend themselves against the zombies. And in turn, they could teach him about the unique aspects of the Dead Rising world, like how to find and use the best weapons against the undead.
I'm not sure if there is an official one, but given the vastness of fanfiction on the internet, it's very likely that someone has written a Naruto - Isaac Dead Space fanfiction. Fanfiction writers love to cross over different fandoms to create unique and often strange stories. They might put Naruto characters in the Dead Space setting, or have Isaac somehow end up in the Naruto world.
In some fanfiction concepts, it could be due to a new, powerful jutsu he discovers or perhaps as a result of some ancient curse or blessing that is bestowed upon him.