Love could be her motivation. Not necessarily romantic love, but the deep friendship and care she has for Harry. She might sense that he's in trouble or just needs her support.
One common theme is friendship. When Ron leaves, it often tests the strength of Harry and Hermione's bond. They might have to re - evaluate what their friendship means without Ron. Another theme is growth. Harry and Hermione usually grow as individuals in these fics. They become more self - reliant and learn new skills or gain new insights.
In such a fanfiction, one possibility is that Hermione leaves the Burrow to bring Harry some important information. Maybe she's discovered a new lead on the Horcruxes. She could be racing against time to reach Harry before Voldemort's forces find out about it too.
One possible reason could be a misunderstanding. Maybe Hermione overhears something Harry says and misinterprets it. For example, if Harry is discussing some dangerous plan with Ron and Hermione thinks he's being reckless without considering her input, she might leave in anger. Another reason could be her own personal growth. She may feel that she needs to explore her own magical abilities further on her own and that Harry's presence is somehow holding her back in that regard.
One popular 'ron leaves harry and hermione fanfiction' could be 'The Unraveling'. In this fic, Ron's departure leads to a series of events that test Harry and Hermione's friendship and their own individual strengths. It shows how they cope with the sudden change and how it affects their fight against the dark forces.
Harry might be initially shocked. He's so used to having Hermione around that her sudden departure leaves him feeling lost. He might start doubting himself, thinking that he did something wrong. For example, he might replay all their recent interactions in his head, looking for signs that he upset her.
One possible reason could be a creative plot twist by the fanfic writer. Maybe they want to explore how Harry would grow and develop on his own without Hermione's support. Another reason might be to introduce new and different story arcs that involve separation, like Hermione having to leave for a dangerous mission that she can't involve Harry in.
One popular 'Harry Leaves Hermione' fanfiction might be 'The Unforeseen Path'. In it, Harry's decision to leave Hermione leads to a whole new set of adventures for both of them. Hermione, left on her own, starts to explore magic in a different way and Harry finds himself in a situation where he has to rely more on his instincts.
Hermione could become withdrawn. She might isolate herself from her friends for a while, spending her time in the library trying to make sense of it all. She might also feel a sense of betrayal, especially if they had some sort of understanding or relationship developing.
Yes, it is a somewhat common plot twist in fanfiction. Some fans like to explore different relationship dynamics. It adds a new layer of drama and can show different character developments that weren't explored in the original books.