Sasuke could also be a main character. He might be initially suspicious of the Kitsune when they enter the ninja world. His sharingan could play an interesting role in detecting and perhaps even learning from the Kitsune's magic. And of course, a wise and old Kitsune elder could be a main character, guiding Naruto or Sasuke in understanding the Kitsune ways.
Kakashi could be a significant character. His vast knowledge and experience would be valuable in dealing with the Kitsune. He could be the one who tries to bridge the gap between the ninja and Kitsune cultures. And a Kitsune princess or prince, who has a special mission related to Naruto's world, could also be a main character, adding a touch of royalty and mystery to the story.
Obviously, Naruto would be one of the main characters. He's the protagonist of the Naruto series and would be the main link to the ninja world in this crossover. Another could be a young Kitsune, maybe one that's just coming of age in the Kitsune world. Their paths cross, and they have to learn to work together.
Maybe another kitsune who has gone bad. In the fanfiction world, there could be a rogue kitsune who sees Naruto as a threat. This antagonist kitsune might be jealous of Naruto's power or his connection to the human world. They could try to undermine Naruto's attempts to protect the village or his friends.
Obviously Naruto is one of the main characters since it's in the title related to him. And the Kitsune, which is likely to be a central figure as the one who needs to be forgiven by Naruto.
It's likely that Naruto would be one of the main characters. He is the protagonist of the Naruto series and would probably be at the forefront of dealing with the Kitsune virus. Sakura might also be involved as she is a skilled medic - ninja and could be crucial in finding a cure. Sasuke could also play a role, especially if his unique powers are somehow related to combating the virus.
I'm not sure specifically who the main characters are in this particular fanfiction without reading it. It could be an original character with Kitsune traits, or it might center around Naruto or other known Naruto characters who have some connection to Kitsune elements.
Obviously, Naruto would be one of the main characters. Since it's about him being the son of a Kitsune, he would be central to the story. There might also be other characters from the Naruto series like Sasuke and Sakura, who could be involved in Naruto's journey regarding his Kitsune heritage. And of course, there could be some original characters created specifically for this fanfiction, perhaps other Kitsune or those who know about Naruto's true nature.
Definitely Naruto himself. He's the main character of the Naruto series, so he has to be there. In a crossover with Attack on Titan, he could meet Eren. Naruto's determination and Eren's drive to protect his people could make for an interesting dynamic between them.
It could be a new genin who has always felt different from the other ninja in their class. This character discovers their kitsune summoning ability during a training exercise and then embarks on a journey to master it.
It could be an evil shinobi who wants to capture the Kitsune Anbu for their unique powers. Maybe they want to use those powers to take over the Hidden Leaf Village. Another option is a rogue Anbu member who has turned against the village and sees the Kitsune Anbu as a threat to their own plans.
It could be another powerful kitsune who wants to use the assassin for their own evil plans. This other kitsune might be jealous of the assassin's skills and wants to control them.
There could be a young and talented Kitsune ninja who is determined to revive the glory of his clan. He would be one of the main characters. And perhaps there are also some characters from other clans who interact with the Kitsune clan members, either as friends or foes. For instance, a Naruto - like character from a different clan who becomes an ally of the Kitsune clan during their rise.