It could be an old, retired Auror. They would have a wealth of practical knowledge about magic and how to use it in dangerous situations. They could teach Harry how to sense dark magic and protect himself better.
Well, one scenario could be that Harry meets a very strict tutor who specializes in Defense Against the Dark Arts. This tutor might push Harry to learn advanced spells and techniques right from the start. Another could be that he gets a tutor for Potions who has a really unique way of teaching, like using rare ingredients found only in Diagon Alley's hidden corners. Maybe the tutor is an old wizard who has a vast knowledge of magical potions and their history.
Maybe it's a new character created by the fanfiction author. This new character could have special abilities or a unique backstory that ties into the reason for escorting Harry to Diagon Alley.
Well, in some fanfictions, it could be due to a powerful spell gone wrong that transfers the ownership to him. Maybe a spell meant to protect Diagon Alley's property rights backfires and suddenly Harry is the owner.
He might have to deal with a lot of administrative work. Running Diagon Alley means taking care of all the shops, making sure the wizards and witches who work there are happy, and dealing with any disputes. For example, if two shop owners have an argument over a piece of land in Diagon Alley, Harry would have to step in and sort it out.
Harry is strolling through Diagon Alley, looking for new robes. He bumps into Daphne near Madam Malkin's. Daphne gives him a cold look at first, but Harry smiles sheepishly. Then Daphne's expression softens a bit as she realizes it's Harry Potter. They start chatting about how difficult it is to find robes that fit just right, and Daphne mentions a little - known shop where she gets her best - fitting robes.
Yes, there are quite a few. You can find them on some popular fanfiction websites like FanFiction.net or Archive of Our Own. Some of these fanfictions explore unique storylines where Harry's upbringing in Diagon Alley exposes him to different magical cultures and characters earlier, leading to some really interesting twists on the original story.
One possibility is that their meeting is not so friendly at first. Daphne, coming from a certain Slytherin - pure - blood mindset, might be a bit haughty towards Harry. But as they talk, Harry's kindness and honesty could break through her initial prejudice. They could end up having a deep conversation about the differences between the houses at Hogwarts, and how they both want to make the most of their time at school, despite their different backgrounds.
One idea could be a story about a young wizard who discovers a hidden, long - forgotten shop in Diagon Alley. Maybe it has magical artifacts that are tied to an ancient prophecy. Another could be a fanfic where a group of students start a secret club in Diagon Alley to practice a new form of magic that's not taught at Hogwarts. Or perhaps a story where a character has to solve a mystery involving a series of strange disappearances in Diagon Alley shops.