It could be that Harry finds out about Dumbledore's secrets regarding the Deathly Hallows. If Harry thinks Dumbledore was more interested in the Hallows for his own purposes rather than for the greater good, it might make him hate Dumbledore.
One possible event could be that Dumbledore fails to protect someone Harry loves dearly. Like if a close friend of Harry's was killed while under Dumbledore's supposed protection, Harry would hold Dumbledore responsible. Another event might be if Dumbledore lies to Harry about his family history. For example, if he hid some important information about Harry's parents that would change Harry's perception of them.
The theme of disillusionment also often appears. Harry, who once idolized Dumbledore, now sees him in a new light. He realizes that Dumbledore is not the perfect mentor he once thought, and this realization leads to his hatred. This can be explored in various ways, such as through flashbacks or interactions with other characters who have different views of Dumbledore.
Yes, there might be some out there. Fanfiction is a vast and diverse world where writers explore all kinds of alternative scenarios. Some writers may create stories where Harry Potter hates Dumbledore for various reasons, such as feeling manipulated or betrayed by Dumbledore's actions. However, this goes against the general relationship portrayed in the original books, which is why it's an interesting and somewhat controversial topic in fanfiction.
Perhaps Dumbledore is shown to have a secret alliance with Voldemort in the fanfiction. Harry stumbles upon evidence of this and is filled with rage and hatred. Or maybe Dumbledore had been manipulating Harry's emotions and actions from the very beginning to fit his own plans for the wizarding world, and once Harry realizes this, his hatred for Dumbledore grows. It could also be that Dumbledore has been hiding a powerful magical artifact that could have saved many lives but didn't, and Harry blames him for it.
This type of fanfic might shift the focus from the fight against Voldemort to the internal conflict between Harry and Dumbledore. It could explore different character traits of both of them that were not as prominent in the original. For example, Harry's potential for anger and Dumbledore's more flawed side.
One reason could be secrecy. If Harry finds out that Dumbledore has been keeping major secrets from him all along, like about his family or his true role in the wizarding world, he might start to hate him. Another reason could be manipulation. If it seems that Dumbledore has been manipulating Harry's actions for his own gain, that would be a valid cause for hatred in fanfiction.
Maybe it's a new character created by the fanfiction author. This witch could have some dark magic tendencies or a past that Dumbledore found unforgivable. For instance, she might have been involved in some unethical magical experiments in the past that Dumbledore strongly opposed.
Yes, there might be. In the vast world of fanfiction, all sorts of creative and unexpected scenarios are explored. Some authors might come up with the idea of Dumbledore being afraid of Harry for various reasons. It could be due to Harry's newfound power that he doesn't fully understand, or perhaps a prophecy that takes an unexpected turn in the author's interpretation. Fanfic writers often like to play with the established characters' emotions and relationships in unique ways.
One possible reason for Dumbledore lying in fanfic could be related to his own past mistakes. He may have thought that by not telling Harry everything, he could guide Harry more subtly towards the ultimate defeat of Voldemort. However, this often creates a sense of betrayal for Harry in the fanfic, which adds a new layer of drama to the story.