Maybe there's a lawyer - like character who tries to get Harry out of jail. This person could be from Harry's old life and is determined to clear his name.
Another character could be a fellow inmate who has been in jail for a long time. He befriends Harry and teaches him the ropes of surviving in jail.
A group of misfit soldiers could be main characters too. They are all a bit different and don't quite fit the typical military mold. But together with Harry, they form a unique unit. There might also be a high - ranking officer who takes an interest in Harry's progress and either helps or hinders him depending on the situation.
Dumbledore could also be an important character. He might be the one who tries to figure out what's wrong with Harry and tries to reverse this hatred. Another character could be Snape. He might see this as an opportunity to make Harry's life even more difficult or, on the other hand, might be secretly trying to help him get over this hatred.
The members of Wildwind would surely be important characters. They could interact with Harry, maybe give him backstage passes or even ask him for his opinion on their new songs.
Well, Dumbledore would most likely be a significant character. He might be one of the few people who quickly understand the implications of Harry being a mutant. He could help Harry navigate through the challenges that come with his new identity. Additionally, there could be some mutant characters from the mutant universe who cross over into the Harry Potter world. For example, a character like Professor X could be an interesting addition, guiding Harry in understanding and using his mutant powers in a responsible way.
Maybe there's a human friend who is really curious about Harry's new situation. This friend could be constantly asking questions and trying to get involved in Harry's alien - related adventures, adding some comedic relief to the story.
There could be his drill sergeant, a tough but fair character who helps shape Harry into a good air force member. Maybe a fellow recruit named Tom who becomes his best friend and they support each other throughout their training.
I don't know for sure as it depends on the specific fanfic. There could be a boss - like character who oversees Harry's work in the unit.
There could be a mentor figure, perhaps an older and more experienced ice elemental who guides Harry in controlling his powers. Another character might be a friend from a non - elemental background who is trying to understand Harry's new identity.
Maybe there's a character named Jack, who is a bit older than Harry and has been on the streets for a long time. He acts as a sort of mentor to Harry, showing him the ropes. And then there could be a young mother named Sarah who is also living on the streets with her baby. Harry might help her out sometimes, and she in turn offers him a sense of family.
It could be Hermione. Since she's Harry's close friend, she would likely play a significant role in a story where Harry is immortal. She might be the one trying to help Harry adjust to his new state or be involved in his adventures in some way.