If Harry Potter lives in Knockturn Alley in fanfiction, it would be a very different story. He could be constantly in danger as Knockturn Alley is full of dark wizards and witches. However, this could also make him more street - smart and better at defending himself. He might learn some spells or potions that are not taught at Hogwarts from the local denizens. And he could have a whole new set of friends or allies who are more on the fringes of the wizarding world.
He might become more cynical. Growing up in Knockturn Alley, he would see a lot of bad things, which could make him less trusting of others.
It would probably be a very dark and gritty take on the Harry Potter story. Knockturn Alley is a place full of dark magic and shady characters. Harry might grow up with a different set of values and skills. He could be more cynical and perhaps have a more ruthless streak in his personality.
In many Harry Potter fanfictions about Knockturn Alley, there are some really interesting shops. One might be a store that focuses on selling items for the Dark Arts, like special robes that have been enchanted with dark magic for concealment or intimidation. There could also be a shop that offers services to repair or modify dark magical objects. Additionally, there may be a place that sells strange and otherworldly substances that are used in the most complex and dangerous dark spells, which are often sought after by dark wizards or witches who are looking to expand their powers in the shadowy side of magic.
Often, we see characters like Draco Malfoy in Knockturn Alley fanfiction. Given his family's connection to the dark arts, it's easy to imagine him frequenting the place. Then there are the shopkeepers of the various dark magic shops, like Borgin and Burkes. And sometimes, even Harry Potter himself might be written into a story set in Knockturn Alley, perhaps on a mission to uncover some dark plot.
One interesting storyline could be a young wizard getting lost in Knockturn Alley and having to find their way out while facing various dark magic items and shady characters. Another could be about a character uncovering a secret illegal potion - making operation in the alley. And there might be a story where a wizard tries to reform some of the dark wizards in Knockturn Alley.
Well, he might encounter a lot of dark and dangerous items. Maybe he'd come across illegal potions or cursed artifacts. He could also meet some unsavory characters who are into the dark arts.
The Dursleys would likely be out of the picture, or at least not as significant. Instead, Harry might be under the care of some dark wizard or witch in Knockturn Alley. His Hogwarts professors would probably view him with more suspicion. His friends, if he made any at Hogwarts from the more 'good' side, would be initially very wary of him.
There could be a fanfic where a young witch or wizard stumbles upon a unique wand in Knockturn Alley. Maybe it has a strange origin or hidden powers. The alley is known for its dodgy dealings, so the wand might be cursed or have a dark history. The protagonist could face many challenges while trying to master this wand.
Well, he could encounter some dark artifacts that have a strange pull on him. Maybe he stumbles upon a cursed object that starts to influence his thoughts in a negative way. Since Knockturn Alley is full of dodgy characters, he might also be recognized by some Death Eaters in hiding, which would put him in great danger.
His character could become more cynical. Dealing with the seedy side of the wizarding world might make him less trusting.