Perhaps a great - grandmother. She could be a very old and powerful witch. She has been watching over Harry from afar all this time. When Harry discovers her, she imparts ancient magic knowledge to him and tells him about the great deeds his ancestors did in the wizarding world.
It could be an uncle. Maybe an uncle who was in hiding all this time because he was afraid of Voldemort. Now that Voldemort is gone, he comes out and reveals himself to Harry. He could have a lot of knowledge about the Potter family secrets and magic that he shares with Harry.
It could be some distant cousins from the Potter family who were thought to be lost in a magical accident.
Perhaps a family of magical scholars. They would expose Harry to all kinds of ancient magic texts and theories. This would make Harry not only a better wizard in terms of practical magic but also in understanding the deeper roots of magic. They could be the ones to finally unlock the full potential of Harry's magic, which was stunted by his difficult upbringing at the Dursleys.
Well, it could be some new students who are very much like the original Marauders in terms of their mischievous nature and loyalty to their friends. Maybe a Gryffindor with a great sense of adventure, a Hufflepuff who is unexpectedly brave and loves to get into fun, a Ravenclaw with a brilliant mind for coming up with pranks, and a Slytherin who has a soft spot for his new group of friends.
In some fanfics, Harry could find out he has distant relatives from the Potter family who live in a far - off land. These relatives could be part of a different wizarding culture. When Harry meets them, he gets to learn about different types of magic and different ways of living in the wizarding world. He might also discover that his family has a much bigger role to play in the overall wizarding history than he thought.
Maybe a house - elf who has broken free from the traditional servitude mindset. This house - elf has developed their own magic in a different way and befriends Harry. They teach Harry about the hidden magic that house - elves possess, which is not taught in regular Hogwarts classes.
Harry Potter himself could be the lead singer. His courage and charisma would make him a great frontman. Hermione could play the keyboard, as she's intelligent and would be able to handle the complex musical arrangements. Ron could be on the drums, providing a solid rhythm. And Luna Lovegood could play the guitar, with her unique and creative personality adding an interesting touch to the band's sound.
One member could be an old, wise wizard who has been living in seclusion for years. He might have a deep knowledge of ancient magic and decides to share it with Harry. Another could be a young witch who is very talented in potions and charms. She could be like an older sister to Harry, helping him with his studies. And there could be a gruff but kind - hearted wizard who is an expert in defensive magic and teaches Harry how to protect himself.
Harry himself would be one of the main members, of course. Hermione could also be part of it, using her vast knowledge of magic to the gang's advantage. Neville might join too, having proven his courage time and time again. And perhaps some of the Weasley twins' friends from their pranking escapades.
It could be the Malfoy family. Imagine Hermione being switched with a Malfoy child. Draco would be in for a huge shock when he realizes that the sister or brother he thought he had is completely different. And Hermione would have to deal with Lucius and Narcissa's pure - blood mania.
There could be a big shift in the power dynamics. If Harry isn't a Potter, some of the alliances and expectations based on his Potter identity would change.