Sure. For example, we can write a story where Fenrir Greyback has been hexed to have a good side. He finds Hermione in a bad situation, like lost in the Forbidden Forest. He takes care of her, provides her with food and shelter. As they interact, Hermione's kindness and intelligence start to affect Greyback. They could end up as allies against a greater evil, and the story can be more about their journey together and how they change each other in positive ways.
One possible plot could be that Fenrir Greyback, for some reason against his usual nature, discovers Hermione in a vulnerable state. Maybe she's been separated from her friends during a battle. He decides to keep her safe from other dark creatures, seeing some sort of potential in her that he doesn't want wasted. He might teach her some of the ways to survive in the wild, which are skills he has as a werewolf.
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.
Hermione would likely react with her characteristic intelligence and courage. She would probably try to use her vast knowledge of magic to find a way to escape or at least resist Fenrir. For example, she might try to use spells that could incapacitate him temporarily. She would also be likely to try and outwit him in conversation, looking for any weaknesses or loopholes in his plans.
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.
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.
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.
There's a fanfiction called 'Greyback's Redemption Arc'. In it, Fenrir Greyback saves Hermione from a group of Death Eaters. The author might have written it to explore the idea of redemption for a character like Greyback. Maybe he saves Hermione because he sees her as a symbol of the good in the wizarding world that he has lost touch with, and this act of saving her could be the start of his journey towards redemption.
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.
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).
One possible plotline could be an alternate universe where Fenrir Greyback is redeemed early on. Maybe he has a moment of self - realization and decides to change his ways. He meets Hermione during this transformation process, and she initially distrusts him but gradually sees his efforts to become a better being. Their relationship could develop as she helps him fully embrace his new, non - violent self.