Perhaps it's about the idea of corruption. Bellatrix, being on the dark side, might be obsessed with Hermione as a symbol of the light side that she wants to taint. In fanfiction, it could be a way to show the struggle between good and evil in a more personal and complex way. Also, Hermione's courage in the face of danger might be something that attracts Bellatrix's attention in these fictional stories.
In fanfiction, Bellatrix's obsession with Hermione could be a result of the latter's unique abilities. Hermione can perform complex magic and has a sharp mind. Bellatrix, who is all about power and magic, might be drawn to Hermione's skills. Additionally, the relationship between the two can add a layer of mystery and drama to the fanfiction, which is very appealing to both writers and readers.
One possible reason could be the contrast between their characters. Lucius is from a traditional pure - blood family, while Hermione is a Muggle - born witch with great intelligence. The idea of these two very different characters interacting in fan - created scenarios might be fascinating to him.
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 reason could be his status as the Boy Who Lived. In the original story, Harry has this special aura about him, and in fanfiction, Hermione might be drawn to that in an obsessive way. Also, his bravery and leadership qualities could be factors that make Hermione overly interested in him.
One possible reason could be that the fanfiction deviated too much from the original character traits of Hermione. Fanfiction often takes creative liberties, and if it strays far from what makes Hermione who she is in the original series, it might make her seem out of character, leading to a decision to leave.
Well, it could also be that Bellatrix is simply bored with the reality of her world in the Death Eater realm. Fanfiction provides an escape into a different world where she can interact with Harry in ways that she may not be able to in the official story. It gives her a chance to be part of new and exciting (to her) adventures that revolve around Harry, even if they are just fictional interpretations created by fans.
It could also be because of relationship incompatibility. Hermione is highly intelligent and driven, and Severus is a complex and often brooding character. Their different personalities might clash in the fanfiction. For instance, Hermione might feel that Severus doesn't support her academic or social pursuits enough, or Severus might find Hermione too outspoken and interfering in his solitary world.
In fanfiction, Hermione's obsession with Harry could stem from her own insecurities. She may see Harry as someone who is more confident and free - spirited. She is obsessed with him as she wants to be part of his world, which seems more exciting compared to her own studious and rule - following nature. Additionally, their friendship has a strong foundation, and the writers of fanfiction might exaggerate this into an obsession to explore different storylines.
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 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.
One reason could be that both the 'Harry Potter' world of Hermione and the 'Percy Jackson' world share elements of magic and adventure. The complex characters and their relationships in Percy Jackson fanfiction might appeal to her. Also, the different interpretations of the Greek mythology in the fanfiction could be interesting to Hermione as she is a very studious character who would likely enjoy exploring new takes on ancient stories.