Well, Voldemort would still be a central character. His actions and the threat he poses could be the very reason Harry is being trained by Death. And then there's Neville. He could be a sidekick of sorts to Harry during this time. Neville might also gain some insights from Harry's training, and together they could form a stronger front against Voldemort. There could also be some new, mysterious characters introduced by the author who are associated with the realm of Death and have their own agendas regarding Harry's training.
I think Sirius Black could be a key character. Even though he's dead, in a fanfiction where Harry is trained by Death, Sirius could come back in some form to offer his support and wisdom. Also, Hermione would surely be involved. She'd be curious about Harry's new training and might try to learn from it herself or help Harry understand the more complex aspects of what he's being taught.
Death, of course, would be a major character as it's training Harry. Maybe Dumbledore could also play an important role. He might be the one who initially guides Harry to this encounter with Death or acts as a moral compass during the training.
Hermione could be a main character. She might be the one who first notices the strange changes in Harry after he becomes friends with Death. She could try to research about this unusual friendship in the library, using her vast knowledge to understand the implications. Ron could also be important. He might be initially skeptical about Harry's new 'friend' but then come to accept it as he sees the positive effects it has on Harry and the help it provides in their fight against dark forces.
Dumbledore would still be an important character. His interactions with Harry, who is raised by Lady Death, would be filled with a lot of mystery and caution. He might try to understand the implications of Harry's upbringing and how it affects the balance of power in the wizarding world. Hermione and Ron could also be main characters. Their friendship with Harry might be strained at first as they try to understand his new and rather dark - influenced personality, but they would still be important in Harry's life as they support him in different ways and help him navigate the challenges he faces at Hogwarts.
Hermione could be there. She would be eager to study the different magics and books in Tamriel. Her intelligence would help Harry navigate the new world.
Hermione could be a main character. As a very intelligent witch, she might assist Harry in his teaching, like helping him prepare complex lessons or providing additional knowledge to the students. For example, when Harry is teaching about ancient spells, Hermione could offer insights from the books she has read.
Hermione could be one. She could come to Degrassi to help Harry. She'd be really good at handling the academic side of things there, like helping students with their studies. And also, she could use her magic knowledge to figure out any magical mysteries.
Besides Harry, death is the central character in this concept. But there could be other magical creatures or beings involved. Maybe thestrals, since they are associated with death in the original Harry Potter lore. They could play a role in facilitating the friendship between Harry and death. And of course, Harry's other friends from Hogwarts, like Neville and Ginny, could also be part of the story, either being curious about or affected by Harry's friendship with death.
Hermione is often involved. Since she's Harry's best friend, she might be the one trying to prevent his death in some fanfictions. Or she could be the one who has to carry on his legacy after he dies.
There could be the leader of the coven. This person might be an old and powerful witch or wizard who has been in the coven for a long time. They would be the one to guide Harry into the ways of the coven.
Megatron could also be a major character. Maybe he views Harry Potter as a threat to his power and plans. He could try to either destroy Harry or use his unique abilities for his own evil purposes. And then there could be Bumblebee, who befriends Harry and helps him communicate with the other Autobots, since Bumblebee is often good at making connections.
Hermione could be a main character. She would use her intelligence and vast knowledge of magic to help Harry plan and build the city. Her skills in research and spell - casting would be invaluable.