There might be a sense of shock as well. It's unexpected and sudden for Bellatrix to take such a physical and menacing stance towards her. This shock could momentarily paralyze her, but then turn into a resolve to resist and not let Bellatrix get the better of her.
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.
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.
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.
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.
One possible plotline could be a story where Narcissa, perhaps having a change of heart in the complex world of the wizarding war, forms an unexpected bond with Hermione. They might start off as adversaries due to their different allegiances but gradually come to understand and support each other in a way that leads to this rather unique physical position as a symbolic representation of their new relationship.
One reason could be pure hatred. Bellatrix despises Muggle - borns, and Hermione being a very intelligent and powerful Muggle - born would be a prime target for her wrath. Another could be jealousy. Hermione's skills and knowledge might make Bellatrix feel inferior, leading her to lash out.
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 in the fanfiction, Bellatrix stabs Hermione as a way to get to Harry Potter. She might think that by harming Hermione, she can draw Harry out and into a trap. Hermione is one of Harry's closest friends, so this would be a strategic move on Bellatrix's part.
One possible motive could be Bellatrix's loyalty to Voldemort. She might think that by kidnapping Hermione, she can get information about Harry Potter and the Order of the Phoenix. Hermione is known to be very intelligent and Bellatrix could believe she has valuable knowledge. For example, Hermione might know the location of Potter or the Order's plans against Voldemort.
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.