Another character Harry could interact with is Xander. Xander, being a normal human in a world full of the supernatural, might be both intrigued and a bit intimidated by Harry. They could bond over their shared experiences of being in over their heads at times. Cordelia might also be in the mix. Her snarky personality could create some entertaining banter with Harry, especially when she comments on his strange wizard ways.
Harry would surely cross paths with Spike. Their interactions would be really fascinating. Spike is a vampire with a complex personality, and his attitude towards Harry, a wizard from another world, could range from hostility to grudging admiration. Also, Anya would be an interesting character for Harry to meet. Her long history and unique perspective on the world of demons and magic could lead to some humorous and thought - provoking exchanges.
Obviously, Buffy would be a major character he'd interact with. They could start off as wary of each other but then grow to respect one another's fighting skills. Giles too, as he has a wealth of knowledge about the supernatural, and he and Harry could have some interesting discussions about different types of magic.
There are many potential characters. The teachers at Forks High School for sure. Harry could have interesting conversations with them. Also, if there are any other supernatural beings in the Forks universe in this fanfiction, like werewolves, he could interact with them. And of course, the students who are into different clubs and activities at the school. He might bond with the science - loving students or those on the school newspaper team, sharing his own experiences from Hogwarts in a veiled way.
One possible plotline could be Harry adjusting to the unique supernatural environment in Sunnydale. He might encounter vampires and other demons that are different from what he's used to in the Harry Potter world. Maybe he forms an unlikely alliance with Buffy and her gang to fight a common, powerful enemy.
Obviously, Harry would be one of the main characters. There could also be local Harlem residents like a street - smart kid who shows Harry around. A jazz singer could be another character, perhaps someone with a mysterious past that Harry gets involved with.
The wizard Gandalf would be an obvious character for Harry to interact with. They are both wizards, though from different worlds. They could share their knowledge of magic, and Gandalf could guide Harry in the ways of Middle Earth while Harry could introduce some new magical concepts to Gandalf.
Obviously, Harry Potter himself. And there could be characters like Hermione and Ron who might either go with him or be involved in some way from afar. There may also be original characters created for Alfe, such as an Alfe wizard who becomes Harry's guide.
Obviously, Harry Potter himself. Then there could be Hermione and Ron, who might visit him at Harvard or communicate with him via magic. There could also be new characters like his Harvard roommate, who could be a normal Muggle but start to suspect that Harry is not an ordinary guy. And maybe some professors at Harvard who take an interest in Harry's different way of thinking.
A potential character could be a reclusive old wizard who lives on the outskirts of the wizarding world. This wizard might have his own reasons for living in seclusion, but when he sees Harry's loneliness, he takes him under his wing. Another character could be a young, orphaned witch who is also trying to find her place in the post - war wizarding world and she crosses paths with Harry.
Obviously, Hagrid could be one. He would be so amazed and probably take baby Harry on little adventures around the Hogwarts grounds, listening intently to what Harry has to say.
One character could be Dobby. Even though Harry is living alone, Dobby might still find a way to visit him and offer his help. Another could be the Hogwarts ghosts. They can pass through walls and might visit Harry in his solitary abode.
He could meet the main characters from Death City. For example, Maka Albarn and Soul Eater Evans. They could be initially cautious around Harry but then become friends as they realize his good intentions.