There could be a magical creature that takes on a human - like form and has black angel wings. This creature could be a guardian of some sort, maybe of an important magical artifact. It might initially be seen as a threat but is actually there to protect the wizarding world. When Harry discovers this creature, they form an unlikely bond, and the black angel wings become a symbol of their unique relationship.
One possibility could be that it's a result of some powerful magic gone awry. Maybe during a spellcasting class or an encounter with a mysterious magical artifact. This new development might lead to him being ostracized at first as others are afraid or jealous. But then he could use his angel wings to his advantage, like flying faster and more stealthily than on a broomstick.
I'm not sure of a specific 'Harry Potter' fanfiction just about angel wings off the top of my head. But you can start by looking on popular fanfiction websites like Fanfiction.net or Archive of Our Own. You can search for the tags 'Harry Potter' and 'angel wings' and browse through the results. There are likely to be some creative and interesting stories there.
It could be his mother, Lily. Her love was already a powerful protection for Harry, so in the fanfiction, it could be her spirit acting as a guardian angel, using her love to shield him from harm in a more direct and continuous way.
His relationship with Hermione would likely become more protective. Hermione, being the logical one, would initially be skeptical but then would research everything she could about the angel wings. Harry would use his wings to save Hermione from danger more easily, strengthening their bond of friendship.
Hermione would probably be both curious and concerned. She'd want to research immediately to find out how and why this happened. Ron, on the other hand, might be a bit more in awe at first. He'd likely make some jokes about Harry looking like a strange bird, but still be supportive.
One possible storyline could be that Harry discovers his angel wings during a dangerous battle at Hogwarts. The wings give him the ability to fly faster and more gracefully than a broomstick, allowing him to outmaneuver the dark forces. He could use them to rescue his friends from precarious situations, like flying them to safety when the castle is under siege.
One possible 'Harry Potter' fanfiction with angel wings could be about a character, perhaps Harry himself, suddenly sprouting angel wings during a dangerous encounter. It might be a magical transformation that gives him new powers to fight against dark forces. For example, the wings could allow him to fly faster than a broomstick and he could use this new ability to escape from Voldemort's clutches or to quickly reach his friends in need.
One idea could be that a new character with black angel wings arrives at Hogwarts. This character might be a mysterious figure, perhaps a guardian sent to protect Harry Potter from a new and unknown threat. Their black wings could symbolize a different kind of magic, not fully understood in the wizarding world. Another plot could involve Harry himself being magically bestowed with black angel wings, which gives him new powers and abilities but also makes him a target of those who fear the unknown in the magical community.
The plot could involve Harry trying to hide his new wings at first. He might be afraid of how the Avengers would react. But then, as the story progresses, his wings could become an asset in a big battle against a common enemy. Maybe the enemy has some sort of anti - flight technology, and Harry's magically - enhanced wings are the key to victory.