One reason could be jealousy. Maybe Ron feels that Harry is getting too close to Hermione and he's afraid of losing her attention. In fanfiction, authors often play with the characters' emotions. Harry, on the other hand, might see Ron as being too possessive of Hermione.
Another possibility is that there's some sort of competition involved. It could be related to who is more worthy of Hermione's love. Harry is the hero who defeated Voldemort, but Ron has been by Hermione's side for a long time. Fanfiction writers might explore this dynamic by creating a fight between Harry and Ron over Hermione.
One reason could be that they might have different interpretations of Harry's character in the fanfiction. Hermione, being logical, may see Harry in a more practical light, while Ron, with his emotional side, could have a different view.
One possible reason could be jealousy. Maybe one of the Weasleys develops romantic feelings for Hermione and the others don't approve or also have feelings for her. Another reason might be related to her magical abilities. If Hermione has some unique magic or knowledge that the Weasleys think can benefit them or their family in different ways, they could fight over it. For example, her knowledge of ancient spells could be seen as a great asset.
In the fanfic, Hermione might regret choosing Ron over Harry because Harry has a different level of understanding when it comes to her academic pursuits. Harry, having faced the challenges of fighting Voldemort from a young age, might have a deeper respect for Hermione's thirst for knowledge and her need to constantly learn and improve. Ron, on the other hand, sometimes showed impatience with Hermione's studious nature.
In fanfiction, Hermione might choose Ron because he represents a more 'normal' life within the wizarding world compared to Harry. Harry was always the 'Chosen One' with a great burden. Ron, on the other hand, was just an ordinary wizard with an ordinary family (despite its quirks). Hermione might have wanted a relationship that was less centered around saving the world and more about day - to - day life at Hogwarts and beyond.
It could be due to a misunderstanding. Suppose Ron overhears a conversation between Harry and Hermione that he misinterprets completely. He might think they are plotting against him or don't really consider him a true friend. So in a fit of anger and hurt, he decides to betray them.
One reason could be love. Hermione is a smart and kind - hearted girl, and the Weasley boys might all develop feelings for her. Jealousy would then be a big factor in their fights.
In fanfiction, Sirius and Remus could fight over Hermione because of their different relationships with Harry. Since Hermione is Harry's close friend, Sirius might think that he should have more influence over Hermione to help Harry better, as he is Harry's godfather. On the other hand, Remus, being Harry's former teacher and friend, also feels a sense of responsibility towards Hermione because of her connection to Harry. This clash of responsibilities and their own personal feelings for Hermione can spark a fight.
One possible reason could be jealousy. Maybe Ron is jealous of Harry's fame and the attention he gets. Another reason might be a misunderstanding. For example, if Harry makes a decision without consulting Ron in a crucial situation, Ron could feel left out and get angry, leading to a fight.
One reason could be envy. Hermione is often very good at academics and magic, and Harry and Ron might be envious of her success. For instance, if Hermione always gets top grades in potions class while Harry and Ron struggle, they could lash out at her out of frustration.
Perhaps they have different ideas about the plot direction. Hermione, being the studious type, may want the fanfiction to follow a more logical and complex plot with Harry involved in solving mysteries or learning new magic. Ginny, on the other hand, might be more interested in a plot that showcases Harry's relationships, especially his relationship with her. So, this clash of interests could lead to a fight.