Well, obviously the vixen would be a main character. Depending on the fanfiction, it could be a powerful and mysterious being with its own motives and backstory.
There might also be other characters from the Naruto series who are affected by Naruto having the vixen contract. For instance, his friends like Sasuke or Sakura. Sasuke might be jealous of Naruto's new power, or Sakura might be worried about the potential risks it brings. Also, characters like Kakashi could play a role in guiding Naruto in dealing with the powers and responsibilities that come with the vixen contract.
The dogs themselves would be very important characters. There could be a lead dog, like a wise and powerful alpha dog that Naruto forms a close connection with. Maybe Akamaru could also play a role, since he is a dog in the Naruto universe already and could be involved in some way with Naruto's new contract.
One interesting aspect could be how Naruto's abilities are enhanced by the vixen contract. Maybe he gains new forms of chakra control or unique jutsu related to the vixen's powers.
Sakura could be one of the main characters. Since she has knowledge of herbs and medicine, she might work with Naruto in his garden to find new medicinal plants. They could have some interesting interactions as Naruto focuses on the growth of the plants and Sakura on their properties.
Sasuke is often a main character in such fanfictions. He could be Naruto's right - hand man, using his skills and intelligence to support Naruto's rule. Their relationship might be more complex, with Sasuke having to come to terms with Naruto's new position of power.
Obviously, the foxes would be the main characters. There could be an old, wise fox that acts as Naruto's mentor among them. It could have a name like Kyo, and it would be the one to teach Naruto the most important lessons.
Well, Sasuke is likely to still be a main character. His relationship with Naruto would be even more complex if Naruto is the son of Apollo. He might be jealous of Naruto's new powers or intrigued by them. Another could be Kakashi. He would play a role in guiding Naruto in understanding and controlling his powers inherited from Apollo.
Sakura might also play an important role. She could be one of the first to notice the changes in Naruto due to his divine connection. Maybe she tries to help him understand and control his newfound abilities, while also dealing with her own feelings for him in this new context.
The demihumans themselves would be important characters. There could be a demihuman leader who Naruto teams up with.
Kakashi could play an important role. His experience and wisdom would be valuable in strategizing against the gods. Additionally, characters like Jiraiya might make an appearance, perhaps guiding Naruto from the afterlife or having left some knowledge that helps Naruto in his defiance. Another character could be Gaara. His unique abilities could be crucial in fighting against the gods' minions.
Kakashi is likely to be a main character too. As Naruto's former teacher, he could be guiding Naruto in the ANBU or having some sort of conflict with the ANBU higher - ups over Naruto's training and assignments.