A common scenario is when Dumbledore lies about Harry's family history. If he hid important details about Harry's parents or their relationship with certain dark forces, Harry would feel betrayed. Another could be Dumbledore giving Harry tasks that were actually much more dangerous than he let on, like sending him into a trap unknowingly.
In some fanfictions, Dumbledore might betray Harry by not being honest about the power Harry possesses. He could be keeping Harry from fully understanding his own abilities for his own purposes. This lack of transparency would make Harry feel used and betrayed. Also, if Dumbledore were to side with the Ministry of Magic against Harry's best interests, that would be a huge betrayal. For example, if the Ministry wanted to control Harry and Dumbledore didn't stand up for him but instead supported their actions in some way.
One scenario is related to the prophecy. Dumbledore could have misinterpreted or misused the prophecy regarding Harry on purpose. He might have made Harry believe that he had no choice but to fight Voldemort, while in reality, there were other options that Dumbledore kept hidden. This would be a major betrayal as Harry's entire life would have been shaped by this false belief. Also, if Dumbledore had a secret alliance with someone who was a threat to Harry and Harry found out, that would make him feel very betrayed.
Another scenario could be that an impostor, using some form of shape - shifting magic, disguises as a Gryffindor and does things that make it seem like Harry has betrayed the house first. As a result, the real Gryffindors, deceived by this false appearance, turn their backs on Harry.
A common plot is that Dumbledore has been manipulating Harry from the start. He might have arranged events in Harry's life to lead him to a specific fate against Harry's will. For example, making sure Harry attended Hogwarts to be part of the fight against Voldemort.
In some fanfictions, Dumbledore might be portrayed as betraying Harry by withholding crucial information. For example, if he knew more about Harry's fate or the true nature of the threats he faced but didn't share it all. This could make Harry feel betrayed as he was left in the dark and had to face greater danger without full knowledge.
In some fanfictions, the betrayal can be a misunderstanding related to prophecy. The camp might misinterpret a prophecy that seems to implicate Percy in something bad. So, they act against him in order to protect the camp, not realizing they are being misled.
One common scenario could be when Dumbledore fails to protect someone she loves. In the fanfic, if her best friend or family member gets hurt due to Dumbledore's inaction, she would hate him. For instance, if there was a dark wizard attack and Dumbledore didn't send enough help.
One possible scenario could be that Harry feels betrayed by Dumbledore for some reason. Maybe he discovers some secrets that Dumbledore has been keeping from him, like the true nature of his family's past or the real intentions behind certain events at Hogwarts. So, in a fit of anger and disillusionment, he decides to ignore Dumbledore.
When Hermione, the voice of reason, betrays Harry because of some newfound 'truth' about him. Harry has always counted on her intelligence and loyalty. So when she turns on him, it's not just a loss of a friend, but also a loss of the one who could have helped him make sense of things. It's like his whole support system crumbles.
One possible scenario is when he meets an ancient and powerful magical being that has just emerged after a long slumber. Dumbledore, in his wisdom, bows to show respect for this being's age - old magic and power. Another could be in a situation where he is facing a group of powerful wizards from a different culture with their own traditions, and he bows as a sign of diplomatic respect.
In such a fanfiction, one possibility could be that Harry Potter defies Dumbledore over the use of certain dark magic items. Maybe Harry believes that Dumbledore is being too cautious and that these items could be used for good in the fight against Voldemort. For example, he might think that the Elder Wand could be harnessed in a different way than Dumbledore anticipates.
In certain fanfictions, Dumbledore's secrets are the root of the perceived betrayal. For instance, his secrets about the Deathly Hallows. If Harry discovers that Dumbledore had known more about the Hallows all along and didn't share this knowledge, which could have changed Harry's journey and decisions, it could be written as a betrayal. Harry may feel that he was used and misled by Dumbledore, and thus the idea of betrayal emerges in these fan - created stories.