One possible consequence could be her transformation into a werewolf. In many werewolf lore within the Harry Potter universe, a bite from a werewolf like Fenrir Greyback often leads to lycanthropy. This would mean that Hermione would have to deal with the monthly transformations, and she would likely face discrimination from some in the wizarding world who are prejudiced against werewolves.
In some fanfictions, she could be ostracized by the wizarding community due to the fear of her new condition. This could lead to her feeling isolated and having to fight for acceptance. Also, it might change her relationships with her friends. For example, Ron might be more overprotective while Harry could be more determined to find a cure for her.
There could be a whole new plotline involving the werewolf packs. Maybe Fenrir Greyback had a specific reason for biting Hermione, and his pack might be involved in some grander scheme. Hermione could be caught in the middle of a werewolf power struggle, having to decide which side to take or how to use her new position within the werewolf community to bring about peace or change.
Well, in some fanfictions, Harry getting bitten by Greyback might lead to a whole new set of adventures. He could be on a quest to find a cure, which would involve seeking out rare magical creatures or ancient spells. It could also change his relationships. For example, Hermione might be more protective of him, while some of his other friends could be a bit more hesitant around him because of the danger his new state poses. Also, it could potentially make him a target for those who want to use his new werewolf abilities for their own evil purposes.
One possible theme is redemption. Maybe the fanfiction explores the idea of Greyback being redeemed through his interaction with Hermione. This could be appealing as it shows the power of goodness (represented by Hermione) over evil.
One possible plotline could be that Fenrir takes Hermione as a hostage to use against the Order of the Phoenix. He might think that her connection to Harry Potter makes her a valuable bargaining chip. Another could be that he is under the control of a dark wizard who orders him to capture Hermione for some dark magic ritual. In some fanfictions, it could also be that Fenrir has some sort of personal vendetta against Hermione and takes her to exact revenge for something she did to him or his kind in the wizarding war.
Well, perhaps in the fanfiction, Fenrir Greyback is under the command of Voldemort to watch Hermione as she is seen as a threat to the Dark Lord's plans. He might follow her around Hogwarts, observing her every move. This could lead to some tense moments where Hermione senses she's being watched but can't quite figure out who it is at first. As the story progresses, she could start to set traps to catch her stalker, which would be Greyback. And there could be a big showdown between them in the end.
She might gain some vampire - like abilities such as enhanced strength, speed, and senses. For example, she could be able to run faster than normal wizards and have better night vision.
Well, it could lead to her being ostracized by some in the wizarding community. People might fear her new werewolf nature, just like they did with Lupin. This could make her feel isolated and struggle with her identity. She might also have to learn to control her newfound instincts, which would be a huge challenge.
Perhaps it's the allure of the 'forbidden'. Fenrir Greyback is a dark and dangerous character, and exploring his relationship with Hermione in fanfiction might be an exploration of the contrast between light (Hermione) and dark (Greyback).
In one fanfiction concept, Greyback saves Hermione when she is trapped in a magical maze created by dark wizards. Greyback, being a cunning and experienced dark creature, is able to navigate the maze and get to Hermione before the maze collapses or she is killed by the various traps inside. He might save her because he senses that she has a great potential that could be useful to him in the future.