A less common but still interesting trope could be the 'time - travel' trope in relation to them. For instance, if Hermione were to go back in time and meet a younger Fleur, or vice versa. This could lead to all sorts of interesting plot developments as they interact with the past or future versions of each other and the events in the wizarding world.
The 'alternate universe' trope is also common. In some fanfictions, the story might be set in a world where the normal rules of the Harry Potter universe don't apply. For example, there could be a world where age differences don't matter as much, or where Remus and Hermione are brought together in a different context, like they are on a secret mission together and their relationship blossoms during that time. There are also stories that might involve time - travel, where Hermione goes back in time and meets a younger Remus, which adds another layer of complexity to their relationship.
A common trope is the 'intellectual connection'. Hermione is very intelligent, and Remus is well - read and knowledgeable. Fanfictions often explore how they bond over books, spells, or complex magical theories. Also, the 'healing each other' trope is quite popular. Hermione can help Remus deal with his lycanthropy - related insecurities, while Remus can support Hermione through her academic or personal struggles.
One popular trope is the 'enemies to lovers' trope. Since Draco and Hermione were on opposite sides in the original series, it makes for a great dynamic in fanfiction. Another is the 'redemption arc' for Draco, where he tries to make up for his past actions and win Hermione over. And of course, the 'forbidden love' trope is also common, given their different backgrounds in the wizarding world.
The 'redemption arc' for Snape is also common. In these fanfictions, Snape's actions towards Harry are often part of his journey to redeem himself. It could involve him realizing his mistakes in how he treated Harry and trying to make it up to him in different ways, which can lead to some really interesting character development and relationship building.
Some fanfictions explore the idea of Hermione being sorted into Slytherin instead of Gryffindor. This changes their relationship as they are in the same house. It can lead to them becoming friends or rivals in a different way than in the original series, and often there are complex relationships that develop between them over time.
One common trope is the 'Forbidden Love' trope. Given Remus's age and his status as one of Harry's teachers, a relationship with Hermione would be considered inappropriate in the eyes of many in the wizarding world. This adds a layer of tension and drama to the story.
One plot idea could be that Fleur starts off subtly trying to befriend Hermione. She might invite Hermione to various Beauxbatons events under the pretense of cultural exchange. Then, as time goes on, Fleur becomes more possessive, getting jealous when Hermione spends time with Harry or Ron. Another idea is that Fleur discovers Hermione's unique magical abilities and wants to keep her close to learn from her and also have her all to herself. Maybe she tries to isolate Hermione from the Hogwarts crowd.
A common theme is 'overcoming differences'. Hermione is a studious Muggle - born witch, while Bill is a more worldly and experienced wizard. Fanfictions often delve into how they bridge the gap between their different backgrounds and personalities. Also, 'helping each other heal' can be a theme. Maybe Bill is dealing with his werewolf bite trauma and Hermione uses her intelligence to assist him, or vice versa.
One popular plot is the redemption arc of Severus Snape through his relationship with Hermione. In these stories, Hermione might see a side of Snape that others don't and help him come to terms with his past actions.
Another plot is a sort of forbidden love story. Given their different allegiances in the original series, a fanfiction might explore how Hermione and Lucius overcome their differences and fall in love. It could involve a lot of tension, secrecy, and internal conflict as they deal with their feelings and the reactions of the wizarding community.