One possibility is that they might have a huge misunderstanding. Maybe they believe Harry has been hiding something dangerous or unethical from them. So in the fanfiction, they decide to abandon him for what they think is the greater good.
In this kind of fanfiction, it could be that Ron and Hermione are being influenced by external forces. For example, a powerful dark wizard might be using magic to make them distrust Harry. Their abandonment could then lead to Harry having to face his challenges all alone, which would make for a very different and perhaps darker story compared to the original series.
Perhaps Ron and Hermione start to pursue their own goals that are in conflict with Harry's. They might think that Harry's continuous fight against Voldemort is putting them in too much danger. Their abandonment would be a shock to Harry, who has always counted on them. This could then set off a chain of events where Harry has to find new allies or rely more on his own inner strength to continue his journey.
One way could be through a misunderstanding. Maybe they believe Hermione has done something wrong, like they misinterpret her actions regarding a dangerous spell she was researching. So they distance themselves from her, which she sees as a betrayal.
In fanfiction, their friendship often develops through shared challenges. For example, when they face a new dark magic threat in the wizarding world, they rely on each other more. Harry's leadership, Ron's humor in tough situations, and Hermione's knowledge combine to make them closer. They also develop their friendship by having deep conversations about their fears and hopes for the future. Maybe Harry shares his concerns about being the Chosen One, and Ron and Hermione support him wholeheartedly.
It could be that Ron and Hermione abandon Harry due to a prophecy that they misinterpret. They believe that by being with Harry, they will bring doom to the wizarding world. So they go into hiding. Harry, on the other hand, is determined to change the course of the prophecy. He embarks on a journey to find the truth behind it, all while feeling the pain of his friends' desertion. He has to fight against dark forces that are taking advantage of the situation.
In such a fanfiction, it might be that Harry and Ron are influenced by a powerful dark spell. This spell makes them see Hermione as a threat, so they abandon her. Hermione then has to find a way to break the spell's influence on them while also dealing with the loneliness and danger she's now in. She could seek help from other Hogwarts students or even some friendly magical creatures.
Hermione, on the other hand, could become more vulnerable yet also stronger. She has always been strong - willed, but this experience could break her down initially. However, as she copes with the miscarriage, she might find new depths to her strength. She could become more in tune with her emotions and learn to lean on Ron more, which is a change from her usually independent self. This new dynamic between them would reshape their characters as they support and grow with each other through this difficult time.
A possible plot could be that the Muggle teacher is being targeted by a dark wizard who wants to use the teacher's knowledge of Muggle technology for evil purposes. Hermione, Ron, and Harry find out and decide to protect the teacher. They have to hide the teacher in the wizarding world and teach them basic self - defense spells.
One possible plot is that a magical object affects Harry and Ron's minds, making them bully Hermione. Hermione, at first, is heartbroken. But she then uses her intelligence to find a way to reverse the object's effect. Meanwhile, she also stands up to them, showing her strength. When the boys are back to normal, they are ashamed of their actions and have to make amends. This could also lead to a deeper exploration of the importance of true friendship and not being easily influenced by external factors.
Perhaps Hermione starts a secret club or organization for students who are interested in advanced magic. As Ron and Harry ignore her, she pours all her energy into this. The club gains popularity and starts to influence the way magic is taught at Hogwarts. Ron and Harry, seeing the positive changes Hermione is making without them, start to feel guilty and try to make amends.
Well, in certain fanfiction scenarios, Ron's jealousy could be a factor. He might feel overshadowed by Harry for so long that it finally drives a wedge between them, and Hermione, being in a relationship with Ron, gets caught up in it. Another possibility is that a prophecy or some ancient magic forces them to make choices that seem like a betrayal to Harry, but they believe they are doing it for the greater good.
There could also be a situation where they are competing with Harry for something, like a powerful magical item or a position in a wizarding organization. In their eagerness to win, they might use underhanded tactics that cause harm to Harry. For instance, they could steal his research notes related to the item, causing him to waste a lot of time and energy, and also feeling betrayed by his friends.