One key element is the contrast between their personalities. Bellatrix is wild and often cruel, while Hermione is logical and kind. Their relationship in these fictions is about how they bridge this gap.
The power dynamics play a huge role. Bellatrix has a lot of power as a Death Eater, and Hermione is a powerful witch in her own right. In 'bellatrix loves hermione fanfiction', they constantly negotiate this power imbalance in their relationship. For example, Bellatrix might try to dominate Hermione at first, but Hermione's intelligence allows her to find ways to equalize the relationship.
Another important element is the setting of the wizarding world. The magical elements, like spells, potions, and the different magical creatures, are often used to enhance the relationship. For instance, a potion could be used to either bring them closer or create a rift between them. The wizarding world's complex social and political structure also affects their relationship. If Bellatrix's actions as a Death Eater put Hermione in danger, it adds more drama and complexity to their relationship in these fanfictions.