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.
In some fanfiction concepts, Bellatrix might be acting on behalf of Voldemort. She straddles Hermione's waist as a way to send a message to the Order of the Phoenix that they can get to their members easily. It could also be a setup for a later rescue or escape sequence where Hermione's friends come to her aid while in this vulnerable position.
Maybe it's part of a magical duel or encounter gone wrong. Bellatrix could have overpowered Hermione during a fight and this is her way of showing she has the upper hand. It could also be a situation where Bellatrix is under the influence of a dark spell or potion that makes her act more aggressively towards Hermione.
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.
She could also be angry. Hermione is a strong - willed character. She might be angry at being put in such a helpless position and determined to fight back somehow, even if she is currently overpowered.
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.
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.
There could be many potential authors. It might be a relatively unknown writer in the fanfiction community who just wanted to explore this unique interaction between Ginny and Hermione.
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.
Perhaps it's a story about a prank gone wrong. Pansy was planning to play a trick on Hermione but ended up in this rather compromising position. It could then lead to a series of events where they have to deal with the embarrassment and the reactions of their friends, and in the process, they start to understand each other better.
One possible plot could be that Bellatrix captures Hermione and tries to torture her for information about Harry. But Hermione, using her wits and some new-found powerful magic she has been secretly studying, manages to turn the tables and kill Bellatrix in self - defense.
Perhaps Bellatrix kidnapped Hermione to use her as bait to lure Harry. Bellatrix has always been extremely loyal to Voldemort and might think that by having Hermione, she can draw Harry out into the open. Hermione, being the intelligent witch she is, could try to outwit Bellatrix while in captivity, maybe by finding a way to send messages to her friends or even by trying to escape on her own.
Well, it could be about a moment of intense emotional connection. Maybe Vicktoria is trying to comfort Bella or they are having a deep conversation in this rather intimate position. It could also be a moment of playfulness between the two characters.