Perhaps in this fanfiction, Harry grows his hair out because he's on a long journey away from the wizarding world. He doesn't have access to hair - cutting magic or tools, and as his hair grows, it becomes a symbol of his growth and the challenges he's facing. He might also discover new magical abilities related to his long hair, like using it as a sensory extension to detect danger.
Obviously, Harry would be the main character. But Hermione could also play an important role. She might be initially against Harry growing his hair out, thinking it's unhygienic or against school rules, but then she comes around and helps him take care of it with some magic hair products she invents.
Well, it could be about Harry and Tom becoming friends as they grow up. Maybe they learn magic together, face challenges side by side, and their friendship changes the course of the wizarding world.
Perhaps the wings grow as a result of some ancient magic that has been awakened within Harry. He could be exploring an old, forgotten part of Hogwarts and accidentally triggers a spell or a curse that gives him wings. At first, he might be scared and try to hide them, but as he learns to control them, he realizes they can be used for good, like helping him rescue trapped students or animals in the Forbidden Forest.
Maybe he wants to change his look to disguise himself from his enemies. In fanfiction, there could be all sorts of threats and he might think a new hair color would help him blend in or not be recognized so easily.
One possible plot could be that they become really good friends. Harry might learn a lot about the Beauxbatons culture from Fleur. They could study together, share secrets, and have adventures in the Hogwarts grounds. Fleur could also help Harry with his French, which could come in handy in some of his later adventures.
Well, perhaps in this fanfiction, Harry grows a beard as a sign of his maturity and the many years of hardships he has endured since defeating Voldemort. Maybe he's living a more reclusive life, away from the spotlight of the wizarding world, and the beard is like a shield from all the attention he used to get. He could be devoting his time to research on ancient magic, and the beard just gives him that wise, old - wizard look.
Maybe it's about a magical spell that causes Harry Potter and the narrator to age in reverse together. They could relive their past adventures in a new way, with the wisdom of their older selves but the energy of their younger selves.
Well, perhaps it could be about Harry growing up in a world where Lily survived. They might have a special bond. Harry could learn magic from Lily in a more personal way, and she could protect him from threats that Voldemort still poses. Maybe they'd have adventures together in the wizarding world, and Lily could introduce Harry to parts of the magical community that he didn't get to experience in the original story.
Maybe Harry is exploring an ancient and forgotten part of Hogwarts when he stumbles upon a magical artifact that causes him to build a cocoon. Once he grows wings from this cocoon, he finds that he has a connection to a long - lost race of magical beings with wings. He embarks on a journey to discover more about this race, all while trying to keep his new form a secret from his friends at Hogwarts who might be afraid of his transformation.
The story could be that Harry grows up alone in the Muggle world, completely unaware of his wizarding heritage until much later. He might face bullying and isolation in the Muggle school. When he discovers his true identity, he has to quickly adapt to the wizarding world all by himself. This could lead to him making some hasty and unwise decisions as he has no one to guide him.