There could also be some unknown characters in the fanfiction. Maybe a secret society within Hogwarts that has been using the cupboard for their own purposes. When Hermione finds out about it, she gets caught up in their affairs. These unknown characters could be students from different houses or even former Hogwarts students who have come back for some hidden agenda related to the cupboard.
In this fanfiction, Hermione might be shocked when she finds out about the cupboard. She could start an investigation to figure out what's been going on in there. Maybe it's a hidden place full of secrets related to Hogwarts' history.
Well, Ron is a given. He's Hermione's significant other, so he'd be deeply involved in the whole process. Luna Lovegood might also make an appearance. She has an unique perspective and could bring some calmness and different kind of support. And don't forget about Hagrid. He has a big heart and might come to offer his congratulations and well - wishes in his own, endearing way.
Other characters like Ginny Weasley could be part of 'hermione fails' fanfiction. Ginny might be Hermione's confidante when she fails in a relationship, offering advice based on her own experiences. Neville Longbottom could also be involved. He could be in a situation where Hermione fails to recognize his potential or she fails to help him when he needs it most. And of course, the Weasley twins, Fred and George, could be involved. They might use Hermione's failure as inspiration for one of their pranks or they could be the ones to cheer her up in a humorous way after she fails something important.
Harry and Ron are likely to be involved. They are her closest friends, and they would surely be there for her during such an important event. They might offer moral support or even help her solve some of the problems related to the test.
Ron is often involved. He's Hermione's husband in many fanfictions, so he'd be there to support her during the birth. Harry might also be present, as he's their close friend. He could be the one to ensure their safety during this vulnerable time. Ginny could be another character, perhaps helping Hermione through the labor process, offering her the kind of female support that's important in such a situation.
She could be shocked at first. Just imagine, she thought she knew her family all this time, and then bam, she's adopted. She might be angry too, especially if she feels she's been lied to. But also, she could be curious and eager to find out more about her real family.
Harry Potter could be involved. He might be caught in the middle of Hermione's revenge plan on Ron. He could try to be the peacemaker, but his attempts might backfire, leading to more chaos between the two. For example, he might accidentally reveal Hermione's plans to Ron, making Hermione even more determined to succeed with her revenge.
Harry Potter often shows up. Since he's their best friend, he might be caught in the middle of their divorce, trying to mediate or just being there for both of them. His presence can add a lot of emotional depth to the story as he struggles with loyalty to both Hermione and Ron.
The truth could also be related to his feelings. Perhaps he's in love with Hermione more deeply than she realizes, and there are some misunderstandings that get cleared up when she finds out. In certain fanfictions, Ron might have been sacrificing his own opportunities for Hermione's sake, like giving up a chance to study with a great wizard so she could go instead.
Madame Maxime, the headmistress of Beauxbatons, would surely play an important role. She might be initially skeptical of Hermione but later come to respect her. Also, there could be a young male wizard at Beauxbatons who is intrigued by Hermione's intelligence and Hogwarts - style magic. He could try to learn from her and in the process, they become friends and face challenges together in the school.