I'm not sure specifically as I haven't read the novel in detail. But typically, the main characters could be the ones directly involved in the relationships with the loved ones. It might be a protagonist who is in a loving relationship with a family member or a romantic partner.
Since I haven't read the 'loved by the twin alphas novel', it's hard to determine the main characters precisely. But if we go by the title, the two twin alphas must be important characters. There's probably also a central character, perhaps a female, who is the object of their love. Maybe there are other supporting characters like friends or family members of the alphas or the loved one that play roles in the story as well.
The main character is probably the one the title refers to - the one fated to be loved by villains. As for the villains, there could be a range of them. Maybe there's a powerful and brooding villain who is initially resistant to the idea of loving the main character but is gradually drawn in. Another could be a more cunning villain who sees the main character as a means to an end at first but then develops real feelings. There might also be a villain with a tragic past that affects their relationship with the main character.
Zoey Redbird is a main character. She's the protagonist who enters the House of Night. Another important character is Aphrodite. She starts as an antagonist but her character evolves throughout the story.
Zoey Redbird is one of the main characters. She is a young girl who becomes a vampyre and has to adapt to the new life at the House of Night. Another important character is Aphrodite. She starts off as a bit of a mean girl but has a more complex personality as the story progresses.
Obviously, Naruto would be one of the main characters. And since it's about being 'loved by kami', the kami itself (though it might not be a traditional character but more of a divine entity) would also be a crucial part. There might also be his friends like Sasuke and Sakura who could play important roles in the story, either supporting Naruto in his new - found relationship with the kami or being a bit skeptical about it.
Morgana can be a very interesting character in fanfiction. She has her own motives and powers, and in some fanfictions, she is explored more deeply, either as a villain with understandable reasons or even as a character who can be redeemed. Writers often play with her character, making her a favorite among those who like complex and morally ambiguous characters.
The main characters are Naruto and Kyuubi. Naruto is the one who has to deal with the power and the presence of Kyuubi inside him. Kyuubi, on the other hand, is not just a source of power but a character with its own personality. In this fanfiction, their relationship is central, and other characters from the Naruto universe might also be involved, but Naruto and Kyuubi are the key focus.
There could be a bear as the main character, and maybe some other forest animals like squirrels or deer that interact with the bear. If it involves humans, then a human character would also be important in the story.