Obviously Naruto would be one of the main characters. There might also be some original characters created for the Western setting, like a Western - style mentor for Naruto or a local hero who teams up with him.
The main character is Naruto, of course. In addition, there may be a female character who is a skilled horse rider and a good shot. She could initially be skeptical of Naruto but later become his ally. And there might be an old wise man in the Western town who helps Naruto understand the ways of the West and gives him advice on how to use his skills in this new environment.
Given the title, Naruto is definitely one of the main characters. But it's possible that new characters will be introduced in the western area he goes to. Maybe there will be a local guide or a powerful adversary in that region.
The main character is Naruto. In the past, he will surely encounter his parents. Minato and Kushina would be important characters in this fanfic. Also, Jiraiya, his mentor, would be a key figure. Since Naruto is going to the past, he might seek Jiraiya's guidance even more. And characters like Orochimaru would also be part of the story as Naruto may try to stop Orochimaru's evil plans earlier.
Obviously, Naruto and Orochimaru are the main characters. Naruto is the protagonist who is going to Orochimaru, and Orochimaru is the one Naruto is going to see.
I can't say for sure without reading it, but Naruto is likely to be a main character given the title. There may also be some original characters created for the Western setting, like a Western - style mentor for Naruto or an antagonist who opposes his claim to be the king of the west.
Obviously, Koyuki herself would be a main character to interact with Naruto. She might show him around her place, introduce him to her people. Also, any of her loyal guards or advisors could interact with Naruto. They could be initially suspicious of him but then grow to trust him as they see his good intentions.
It could be about Naruto's adventures in a Western - style setting. Maybe he uses his ninja skills in a world similar to the Wild West, facing new enemies and challenges.
Naruto is surely a main character. There could be new characters created specifically for this fanfic as well. For example, local leaders or warriors in the west that Naruto has to deal with. Maybe there's a character who helps him when he first arrives in the west and becomes his right - hand person. And of course, we can't rule out the possibility of some of Naruto's old enemies showing up in this new setting to cause trouble for him.
He could meet some new and powerful shinobi who have different fighting styles compared to those in the Hidden Leaf. For example, some shinobi who are experts in wind - based jutsus that are unique to the western regions.
Obviously Naruto is one of the main characters as the title 'naruto goes blind fanfiction' implies. His friends like Sasuke and Sakura are also likely to be main characters. They play important roles in Naruto's life, especially when he's dealing with his blindness. They could be his support system or even be part of the conflict in some cases.