Maybe a young American witch named Lily (not related to Harry's mother) who becomes his friend. She could be very curious about his foreign - sounding spells and they could learn from each other.
There could be an American wizard who takes Harry under his wing, like a gruff but kind old wizard named Alistair. He could teach Harry about American magic in a no - nonsense way.
Potential new characters might include a young American wizard called Tommy. He's a bit of a troublemaker but has a good heart. There could also be an old and wise American wizard professor, Professor Anderson, who teaches Harry about the history of American magic. And then there's a female wizard, Sophia, who is very interested in the British magic system and befriends Harry to learn more.
Some potential new allies could be the house - elves. They might see Harry's plight and decide to help him, using their unique magic and knowledge of Hogwarts' secrets. Another could be the centaurs in the Forbidden Forest. They are very wise and may take Harry under their wing.
There could be a wise old wizard who has knowledge about the true nature of the Master of Death and becomes Harry's mentor. Maybe a powerful magical creature that is drawn to Harry's power and offers its assistance.
Another potential set of new characters could be ancient wizards or witches who were once associated with the concept of the master of death. They could come back to either guide Harry or challenge his claim to the title. This would add a lot of depth to the story as Harry would have to prove himself to these predecessors or learn from their experiences.
One potential new character could be an old hermit - like wizard who has been living in the woods near the manor. He has a deep connection with the land on which the manor stands and can communicate with the spirits of the forest. He could be a source of ancient wisdom for the main characters. Also, a young and adventurous witch who is on a quest to find a lost magical gem that is rumored to be hidden somewhere in the manor. She could bring a new dynamic to the group with her fearless and independent nature. There could also be a magical gardener who takes care of the manor's enchanted gardens and has some secrets of his own.
There could be a dark arts teacher who is actually a double - agent. This character might seem to be teaching Harry the wrong things at first but is actually guiding him to use the Dark Arts for good. Another new character could be a mysterious figure from an ancient dark arts cult who tries to recruit Harry for their own purposes.
An American wizard detective. He could be investigating strange magical happenings in the wizarding world of America. The Potter character could cross paths with him and end up teaming up to solve a big case.
A new young teacher at Hogwarts. She could be a prodigy in Transfiguration, having mastered some really advanced spells at a young age. She brings a fresh perspective to teaching and has a bit of a rivalry with McGonagall in the fanfic. She might also have a mysterious past that is gradually revealed throughout the story.
A mysterious Pokémon whisperer might appear. This character could have the ability to communicate with Pokémon in a unique way and help Ash better understand his Pokémon, which in turn helps him grow as a trainer during his time without his friends.
Obviously, Harry Potter himself would be the central character. Then, Hermione Granger could be one of the members of the harem. She is intelligent and has a long - standing friendship with Harry. Ginny Weasley is also a likely candidate as she has a romantic interest in Harry in the original series. Luna Lovegood might be another, with her unique and dreamy personality adding an interesting dynamic to the harem.