Perhaps Dumbledore has some magical means to detect Harry's past traumas. In the wizarding world, there could be spells or potions that can reveal hidden emotional scars. Dumbledore, being a very powerful and observant wizard, uses such methods to find out about Harry's abuse.
Maybe he notices Harry's unusual behavior, like being overly withdrawn or flinching at sudden movements. That could be a sign that makes Dumbledore suspect abuse.
It could be that other characters in the fan fiction, who are close to Harry, notice something amiss and inform Dumbledore. For example, Hermione might pick up on some emotional distress in Harry and tell Dumbledore about it. Then Dumbledore starts to investigate and discovers the abuse.
Dumbledore could start providing Harry with special magical training to help him build confidence and defend himself, not just from physical threats but also from the emotional aftermath of the abuse. He might also arrange for some sort of therapy within the wizarding world, like using magical creatures or spells to heal Harry's emotional wounds.
Well, Dumbledore has always had a special connection with Harry. When he finds out about the abuse, he would be devastated. His first instinct would be to comfort Harry. He might also reflect on his own actions and whether he could have prevented the abuse from happening. Dumbledore would then use all of his resources to make sure Harry is safe and happy. He could provide Harry with a mentor or a guide to help him through the difficult times, someone who can teach Harry how to cope with his past and move forward in a positive way.
Harry's life would likely become more stable. He might get proper care and attention, which could improve his academic performance at Hogwarts. Also, he could start to make more friends as he is no longer burdened by the secrecy and pain of the abuse. Dumbledore might arrange for him to have some kind of therapy within the wizarding world to deal with the emotional scars.
Dumbledore, as Harry's guardian in the fanfiction, would probably use his influence in the wizarding world. He could make sure that Harry is taught by the best teachers at Hogwarts. He'd also be there to offer advice and guidance, especially when Harry faces challenges like dealing with Voldemort or other dark forces. For example, he might teach Harry some advanced defensive magic privately to better protect himself.
Harry might initially be confused. He has always looked up to Dumbledore, so when he realizes Dumbledore is trying to control him, he could start to question everything he thought he knew about their relationship. He may become more rebellious as a result, trying to break free from Dumbledore's influence and make his own decisions.
It might make Harry more confident. With Dumbledore's training, Harry gains more knowledge and skills, which gives him the confidence to face challenges.
He becomes more nurturing. Dumbledore, who was mainly seen as a wise leader, now has to be a caregiver. He might show more patience and tenderness as he takes on the role of a father to Harry.
The relationship would become very strained. Harry's rejection would likely make Dumbledore re - evaluate his actions and how he has interacted with Harry. Dumbledore might be shocked at first, since he probably thought Harry was on the same page as him most of the time.
As the story progresses, Dumbledore might try to make amends. He could start revealing some of his secrets to Harry in an attempt to regain his trust. Harry, on the other hand, would be hesitant at first but gradually start to listen and understand Dumbledore's reasons.
The fanfic changes the perception of Dumbledore's character in that it shatters the image of his infallibility. He is no longer the perfect headmaster and guide. Stealing from Harry shows that he is capable of moral wrongs, and this can lead to a more nuanced understanding of his character, where he is not simply all - good or all - bad but a mix of both, with his own motives and desires that might not always align with what is best for Harry.