In the 'Harry Potter can't walk fanfiction' when Harry loses his ability to walk, the story could develop in a very emotional way. His friends and allies would be determined to find a way to restore his ability to walk. Meanwhile, Harry himself might start to see the wizarding world from a different perspective. He may notice things that he overlooked before when he was able - bodied. He could also become a symbol of perseverance for other students who are facing difficulties. The story could also involve Harry learning to use magic in new ways to compensate for his lack of mobility, such as using telekinesis spells more effectively.
Well, his friends might rally around him. Hermione would probably start researching every possible spell or potion to help him. Ron, on the other hand, would be there to offer moral support and practical help like getting Harry around. For instance, he could use a levitation charm to move Harry from place to place.
One possible reason could be that he was injured during a battle with dark wizards. Maybe he was hit by a powerful curse that affected his legs. Another reason might be related to some kind of potion gone wrong. For example, if he accidentally drank a potion that had negative side effects on his motor functions.
The story could develop with Harry being shunned by some in the wizarding community. They might see him as a has - been or a disappointment. But he might also find a small group of allies who believe in him regardless of his lack of magic. They could help him find new ways to contribute to the fight against evil, like using his knowledge of magic to outwit dark wizards even without being able to perform spells.
He would become more humble. Losing his magic would make him realize that he's not invincible. He'd start to value the people around him more. For instance, he'd be more grateful for Hermione's intelligence and Ron's loyalty.
Harry might walk away because he has a new mission that he can't share with others. He realizes that to protect the wizarding world in a more fundamental way, he has to go it alone. So, he quietly walks away from his normal life to pursue this unknown and dangerous task.
Well, it might develop as a result of some new magic he encounters. There could be an ancient spell or a magical artifact that gives him the power to control sand. He then has to figure out how to use it. He may start with simple things like making sand swirl around his hand, and as he gets more used to it, he can do more complex things like creating sand barriers or even using the sand to communicate in some way.
He could become more confident. With the new resources from his inheritance, he feels more secure in his place in the wizarding world. For instance, if he inherits a lot of gold, he doesn't have to worry about financial problems at Hogwarts.
In some cases, he could become a puppet for the dark side. Without his soul, he has no moral compass, so he could be easily manipulated by the forces of evil to do their bidding. His friends would then be in a race against time to restore his soul before he causes too much harm.
Well, it might start with Harry having doubts about his parents. Then, as he digs deeper into their past, he could start to distance himself. Eventually, he publicly disowns them, which would shock the wizarding community. This could lead to him being ostracized by some and supported by others who also have doubts about his parents' actions.
Maybe he accidentally finds out when he is near some magnetic objects in Hogwarts. For example, he might notice that he can make the metal keys move towards him without using magic spells he already knew. It could be during a time when he is exploring an old, forgotten part of the castle where there are a lot of metal objects and strange magnetic fields.