One possibility is that it's a story exploring a new kind of friendship or bond between them. They could be in a magical training session and Fleur straddling Hermione's hips is part of a new spell - casting technique they are learning together. Or perhaps they are in a dance or some kind of cultural exchange within the wizarding world that involves this rather unique physical position.
In the fanfiction, it could be that they are in a competition of some sort, like a magical dueling competition where Fleur has to immobilize Hermione for a moment and this is the position she ends up in. It could also be related to a plot where they are both under the influence of a strange magical charm that makes them interact in this way, and the rest of the story is about how they break free from the charm and what they learn from the experience.
Well, it could be a story about a deep emotional moment between Fleur and Hermione. Maybe they are in a situation where they are comforting each other or having a very intense conversation. It might also be part of a magical adventure where they are in a dangerous situation and this physical closeness is a result of trying to protect each other.
Obviously, Fleur and Hermione. Fleur, with her Veela heritage, might have some unique magical properties that come into play in the situation described. Hermione, on the other hand, will likely use her quick thinking and vast knowledge of magic to deal with whatever situation they are in. Their relationship in this fanfiction could range from being rivals to becoming close friends or allies.
One possible plot could be a story set during a Triwizard Tournament - related event. Maybe Fleur and Hermione are forced to work together in a dangerous task and during a moment of panic or urgency, Fleur straddles Hermione to protect her from some sort of threat. And from there, a new bond forms between them.
Well, it could develop into a story of deep friendship. Maybe Fleur was trying to comfort Hermione during a difficult time. They might start sharing their secrets and fears, and through this physical closeness, a strong bond of sisterhood could form.
Well, it could be about a moment of intense friendship or perhaps a situation where Ginny is trying to protect Hermione. Maybe they are in the middle of a fight or some kind of magical accident and Ginny's position is one of immediate reaction to help Hermione.
I'm not sure where you can specifically find a fanfiction with this description. You could try popular fanfiction websites like Archive of Our Own (AO3) or FanFiction.net. Search using the names 'Fleur' and 'Hermione' along with relevant tags such as 'relationship' or 'interaction' to narrow down your search.
One possible plot could be that Bellatrix is trying to intimidate Hermione. In many fanfictions, Bellatrix is a menacing character. She might straddle Hermione's waist to assert her power and dominance, perhaps during an interrogation where she wants to break Hermione's spirit and get information from her.
One possible plot could be that Hermione, as a Lycan, struggles to hide her identity within the Hogwarts community. Fleur, being perceptive, might notice something off about Hermione. Maybe Hermione is afraid of being discovered and ostracized, while Fleur, having her own experiences with being different (as a Veela), tries to help Hermione come to terms with her new lycanthropy. They could form a strong bond as they both deal with the challenges of being 'other' in the wizarding world.
Well, it could start with Hermione realizing her deep feelings for Fleur. Maybe she plans a very elaborate and romantic proposal. She might choose a special place like the Hogwarts grounds under a full moon. Fleur could be initially shocked but then really touched by Hermione's boldness.
Perhaps the plot could involve a love triangle. There could be another character, like Viktor Krum, who still has feelings for Hermione and is jealous of her relationship with Fleur. This would add drama and tension to the story. Also, Fleur's family might not approve of Hermione, leading to more conflict.
One possibility could be a situation where Fleur is under the influence of a dark spell. Maybe she's been hexed to do this to Hermione. In the fanfiction world, this could be a lead - up to a rescue mission by Harry and Ron. They would have to figure out how to break the spell on Fleur and free Hermione.