Sure, it's possible. In the world of fanfiction, all kinds of pairings are explored. This particular one could lead to some very intense stories. For example, it could show how Hermione, with her intelligence and magic skills, copes with being Fenrir's mate. It might also delve into the werewolf lore within the Harry Potter universe more deeply, like how their relationship affects Fenrir's lycanthropy and Hermione's standing in the wizarding world.
One possible plot could be that Hermione discovers she has some sort of connection to Fenrir through a magical bond. She initially resists it due to his dark nature but as she gets to know him better, she realizes there is more to him. Maybe she tries to help him control his werewolf side and in the process, they develop a relationship that is frowned upon by the wizarding community.
I'm not sure if there is such a specific fanfiction. It seems like a rather dark and unusual pairing considering Fenrir Greyback is a werewolf known for his brutality. However, the world of fanfiction is vast, and there might be some out there that explore this concept, but it's not a common or mainstream idea in the Harry Potter fanfiction community.
There's also 'Hermione and Fenrir: A Different Kind of Magic'. This story focuses on the cultural and magical differences they have to overcome as they form their bond. It shows how Hermione's intelligence and Fenrir's wild nature interact in a unique way. The author does a great job of creating a believable relationship between the two characters within the wizarding world's context.
One common theme could be the struggle between different magical worlds or ideologies. Since Fenrir is often associated with the darker side of the wizarding world and Hermione is a very 'light - side' character. Another theme might be the exploration of an unlikely relationship, as their personalities and natures seem quite different.
I'm not sure of specific 'fenrir and hermione mate fanfiction' titles off - hand. You could try searching on fanfiction - dedicated websites like Archive of Our Own. They usually have a large collection of such fan - created stories.
A fanfiction with Hermione as Fenrir Greyback's mate would likely be a complex exploration of two very different characters. Hermione would bring her knowledge, determination, and moral compass to the relationship. Greyback, with his werewolf instincts and violent past, would be a contrast. It could show how Hermione might try to civilize Greyback, or how she copes with being associated with such a feared figure. The story could also involve the reactions of other characters like Harry and Ron, who would surely be horrified. It might also explore the werewolf society and how Hermione fits into it, all while dealing with the power dynamics between her and Greyback.
In the fanfic, it might lead to a story where Fenrir tries to protect Hermione in his own way. Since she's his mate, he could see her as something precious to him. This might put him at odds with other dark forces in the wizarding world who might want to harm Hermione for various reasons. It could also cause a stir among Hermione's friends, like Harry and Ron, who would be very suspicious of Fenrir's intentions towards her.
In the wizarding world, Hermione is associated with the light side and Fenrir with the dark side to some extent. For their relationship to work, they would have to bridge this gap. Maybe Fenrir could be redeemed through Hermione's love and influence. Hermione, on the other hand, would have to accept Fenrir's werewolf nature, which might put her in danger. It would be a relationship full of challenges and sacrifices, but also one that could potentially change the way the wizarding world views werewolves.
One key theme could be the struggle between different magical natures. Hermione is a highly intelligent and rule - abiding witch, while Fenrir is a werewolf often associated with chaos. Their 'mating' in fanfiction might explore how they overcome these differences. Another theme could be the idea of redemption for Fenrir through his relationship with Hermione.