Hermione is the central figure in 'hermione learns her place fanfiction'. However, antagonists can also be main characters in a sense. For example, students who bully or oppose Hermione because of her intelligence or her attempts to break the status quo could be main characters. They create the conflict that forces Hermione to reevaluate and learn her place. And of course, Hermione's family, if they are involved in the story, can be important characters too, as they are part of her identity and influence her perspective on her place.
The main character is Hermione. But other characters from the Harry Potter universe can also be main characters in this fanfiction. Characters like Draco Malfoy could be significant. His snobbish attitude towards Hermione and others might be a factor in her learning her place. The ghosts of Hogwarts could also play a role. They are part of the Hogwarts environment, and their unique perspectives could add to Hermione's understanding of her place in the magical world.