Well, he might be really confused at first. Fanfiction often takes the original story in different and sometimes wild directions. He could be shocked to see how some fans have imagined his relationships or new adventures that are quite different from his own experiences.
In some fanfictions, Harry Potter might learn some hidden secrets about the wizarding world's economy from the goblins. The goblins are known for their control over Gringotts and have a deep understanding of magical treasures. Harry could discover a new plot against Hogwarts related to a valuable artifact hidden in the vaults.
Maybe Harry discovers a new type of snake with magical abilities. For example, it could be a snake that can turn invisible at will. This would be really cool as it could add a new dimension to the wizarding world's magical creatures.
Perhaps Harry Potter talks to the dragon to enlist its help in finding a powerful magical object. Dragons are known to guard treasures. He could be on a quest for a Horcrux or some other important item. The dragon might initially be hostile but as they talk, it starts to trust Harry. Their conversation could involve exchanges about the power of magic, the dragon's own experiences in the magical world, and how they can both benefit from working together.
One interesting scenario could be Harry having a conversation with the Whomping Willow. He could find out why it's so aggressive and maybe even convince it to be more friendly. Another could be him chatting with the house - elves through the rats or other small animals that might be in the kitchen. He could learn more about their secret world and their hopes and dreams.
Well, he might try to tame the dragon. In some fanfictions, Harry could use his magic skills to communicate with the dragon on a deeper level, perhaps to gain its trust and make it an ally.
Well, he might be tempted by the dark magic within the Horcrux. It could try to manipulate him, maybe show him false visions of power or ways to defeat Voldemort that are actually leading him astray.
Well, it could be that the magic book is sentient and starts to communicate with Harry. It could offer him advice on how to defeat Voldemort in a completely new way, like revealing a long - forgotten prophecy.
In this fanfiction, Harry could become a sort of living magic conduit. He could be able to manipulate magic in ways that are unheard of. He might be able to merge different spells together to create entirely new and powerful incantations. And perhaps he could use his new oneness with magic to heal the most serious of magical ailments with just a touch.
In such a fanfiction, Harry might discover ancient spells that give him an edge in battles. For example, he could learn old defensive magic that can protect Hogwarts in a more powerful way than the existing spells. He might also use old magic to communicate with long - lost magical creatures that hold secrets of the wizarding world.
In this kind of fanfiction, Harry might feel extremely lost and depressed. He has been defined by his magic for so long, and without it, he'd have to re - evaluate his identity. Maybe he'd start to rely more on his friends, like Ron and Hermione, in different ways. For example, instead of using magic to solve problems, he'd have to use his wits and their combined non - magical skills.