One interesting plot could be Hermione trying to use her intelligence to outwit Fenrir Greyback. Maybe she's on a mission to rescue someone he's captured, and she has to use her magic skills in new and creative ways. For example, she could use a combination of transfiguration and charms to create distractions while she sneaks around his lair.
A third plot could be a time - travel scenario where Hermione goes back in time and tries to prevent Fenrir Greyback from becoming the werewolf he is. She could try to change his past, but in doing so, she unknowingly alters the present in unexpected ways. This would lead to a lot of drama as she tries to fix the changes she's made while still dealing with Fenrir.
One interesting storyline could be Hermione using her intelligence to outwit Fenrir Greyback. For example, she could create a spell or potion that repels werewolves like him. Another could be a scenario where Fenrir tries to capture Hermione for some dark purpose, but she manages to turn the tables on him with the help of her friends. Maybe she could also find a way to cure Fenrir's lycanthropy, leading to a change in his character.
There could also be a fanfiction where Hermione Granger is forced to face Fenrir Greyback alone in a dangerous situation. This would showcase her bravery and her ability to use her magic skills under extreme pressure. The story could focus on her mental and magical struggle against Greyback, perhaps with her using some of the more advanced spells she has learned over the years to defend herself and those around her from the werewolf's attacks.
You can start by looking on popular fanfiction websites such as Archive of Our Own (AO3). AO3 has a vast collection of fanfictions from various fandoms, and there's a good chance you'll find some Hermione Granger x Fenrir Greyback stories there. Just use the search function and type in the relevant tags.
Another storyline might involve a time - travel scenario where Hermione goes back in time and encounters a younger Fenrir Greyback. She attempts to change his path, to prevent him from becoming the cruel werewolf he is known to be in the future. This could involve her using her knowledge and magic to offer him a different future, but facing many challenges along the way.
In some fanfictions, the relationship is portrayed as one of pure enmity. Fenrir Greyback, being a cruel and savage werewolf, is seen as a threat to Hermione. He represents the dark and violent side of the wizarding world that she is constantly fighting against. His predatory nature towards her, especially given her Muggle - born status, makes for a very tense and hostile relationship.
The contrast between the two characters. Hermione is a brilliant, studious witch, while Fenrir is a savage werewolf. This contrast can lead to some really interesting character dynamics in fanfictions.
A possible plot is that Hermione, in her pursuit of equal rights for magical creatures, decides to reach out to Fenrir Greyback. At first, he is hostile, but Hermione's determination and her ability to see beyond his monstrous side start to change him. They could end up in a situation where they have to work together to stop a greater evil that is targeting werewolves and other marginalized magical beings. This would involve Hermione using her logical thinking and Fenrir using his knowledge of the werewolf underworld.
For Hermione, her development could involve facing her fears of werewolves like Fenrir. She might start off being very cautious and perhaps a bit prejudiced due to his reputation. But as the story progresses, she could learn to look beyond the surface and see the complex person (or creature) that Fenrir is. This would show her growth in empathy and open - mindedness.
One plot idea could be that Fenrir, in his 'good' form, helps Hermione in her research on werewolves. He uses his insider knowledge to guide her in understanding the complex nature of lycanthropy, and they form an unlikely alliance against those who want to use werewolves for dark purposes.
One idea could be that Fenrir Greyback, instead of being a full - on villain, has some sort of complex relationship with Hermione. Maybe he's forced to protect her in a situation where they are both in danger from a greater dark force. This could lead to a lot of tension and moral dilemmas for Hermione as she has to deal with being around a werewolf who has a reputation for being cruel.