One possible theme could be power dynamics. Bellatrix is a Death Eater with a lot of power and Hermione is a brave and intelligent witch. The act of Bellatrix playing with Hermione's tie can show the power imbalance between them.
Another theme might be psychological manipulation. Bellatrix is known for her cruel and unpredictable nature. By playing with Hermione's tie, she could be trying to get into Hermione's head, make her feel vulnerable and uncertain. This can be a theme about how psychological games are played in a world of magic and conflict.
The theme of identity could also be present. Hermione's tie is part of her Hogwarts uniform, which represents her identity as a student and a member of the wizarding world fighting against the dark side. Bellatrix messing with it could be seen as an attack on Hermione's identity and values.
Well, it could also be that Bellatrix is using the act of playing with Hermione's tie as a way to show her dominance. Since Bellatrix is a rather cruel and powerful character in the Harry Potter universe, this small act could be symbolic of her lording over Hermione, who is seen as a symbol of the resistance against the dark forces.
Another motive could be related to Bellatrix's loyalty to Voldemort. Maybe she suspects Hermione of something, and this is her way of getting a reaction out of her. She could be trying to unnerve Hermione to see if she gives away any secrets or shows signs of being involved in something that Bellatrix or Voldemort would be interested in.
This moment can also lead to a more complex dynamic. Hermione might become more determined to oppose Bellatrix, not just because of their ideological differences but also because of this personal affront. And Bellatrix may see Hermione as more of a worthy opponent or a nuisance that needs to be dealt with more harshly, which would drive more interactions and conflict between them in the fanfiction.
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 theme could be transformation. For example, the horse might symbolize a transformation in Hermione or Bellatrix's journey. Maybe it represents a new power or a change in their relationship.
Fanfiction often plays with established characters in new and unexpected ways. Regarding Hermione being Bellatrix's sister, it could be part of a parallel universe concept. In this alternate reality, the rules of blood relations in the wizarding world are different. The author could be using this idea to show how different circumstances can shape a character. For example, Hermione might have some of Bellatrix's fierceness if they were sisters, or Bellatrix could have some of Hermione's intelligence, which would make for a very interesting story.
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.
Survival is a prevalent theme. Given Bellatrix's murderous and unpredictable nature, Hermione often has to fight for her survival in these fanfictions. It could be a physical fight, or a mental battle as she tries to outmaneuver Bellatrix in a dangerous situation.
A common theme is power struggle. Bellatrix is a powerful and dark witch, and Hermione is also very powerful in her own way with her intelligence and magic skills. So, there's often a back - and - forth as they try to assert their influence over situations or each other.
Well, a major theme would be oppression. Bellatrix is a cruel character, and Hermione being her slave would mean facing a great deal of oppression. There could also be a theme of hope. Hermione would probably hold onto the hope of escape or liberation. Additionally, the theme of the corrupting influence of power might be present. Bellatrix's power over Hermione could lead to her becoming even more sadistic and Hermione having to find ways to not be broken by it.