He gave Harry a sense of purpose. By revealing bits of Harry's past and the prophecy, Dumbledore made Harry understand his role in the fight against the Dark Lord.
Dumbledore also introduced Harry to a network of allies. Through Hogwarts and his own connections, he made sure Harry had friends and supporters like Hermione and Ron to help him grow and face challenges.
The Ministry of Magic would probably be in an uproar. They might see Dumbledore's actions as a blatant abuse of power. They would send out Aurors to search for Harry and arrest Dumbledore. After all, Dumbledore is one of the most powerful wizards, and his actions would be seen as a threat to the stability of the wizarding world.
Some would be in shock and disbelief. People who idolized Dumbledore would initially refuse to believe Harry's claims. They would think Harry was either misinformed or had some malicious intent.
The wizarding world in the fanfiction might be in chaos. People who idolized Dumbledore would be shocked and perhaps feel betrayed. There could be a lot of gossip and rumors flying around. Some might even start to question other things Dumbledore has done in the past.
Dumbledore could gain new insights. Fanfiction might explore the social aspects of the wizarding world in ways he hadn't considered. Maybe there are stories about how the different houses interact in a more complex way than he thought. This could make him reevaluate his own views on the unity or division within Hogwarts.
It expands it. Fanfiction often shows new styles of clothing and accessories that weren't in the original books. This makes the wizarding world seem more diverse and full of possibilities in terms of aesthetics.
If the character was a scientist in their previous life, they might try to apply scientific methods to magic. For example, they could experiment with different ingredients for potions in a more methodical way.
The portraits can act as a source of emotional support. Just seeing their faces and the expressions of love and pride on them can boost Harry's confidence. For example, when he's feeling down about his latest encounter with Voldemort, a glance at their portraits might give him the strength to keep going.
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.
His Apparition skill could be useful. He could quickly get fresh ingredients from far - off places. Also, the levitation charm would help him in handling multiple pans and utensils at once. Magic could also help him in precise measurements and temperature control without the need for normal kitchen gadgets.
Some in the wizarding world would be excited. The French wizarding community might see it as a great connection to the famous Harry Potter from Britain. They would celebrate the union as a way to strengthen the relationship between the two magical communities. However, there might also be some who are skeptical. Some traditional British families might think it's a bit odd as they don't know much about Apolline. But overall, most of Harry's friends would be happy for him and look forward to the new cultural exchanges that would come with the marriage.