He could meet a young and brilliant wizard inventor. This inventor is working on some newfangled magical gadgets and shows Harry some prototypes, like a self - flying broomstick that can change its shape according to the rider's mood.
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.
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, he could meet some new and mysterious characters. Maybe a young wizard with a strange power who becomes his friend or an old wizard with a hidden agenda. He might also discover a new magical shop that sells unique items not found in the regular Diagon Alley stores.
Well, he might encounter a new magical creature that is not in the original books. For example, a tiny dragon that can speak and becomes his little friend, guiding him through the Alley and showing him some hidden shops.
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.
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.