The 'dark child' is likely to be a main character. In addition, there could be characters from the child's family, whether they are good or bad influences. There might also be some Hogwarts professors who play important roles. For instance, Professor Dumbledore could be involved, either trying to protect the child from the darker forces or trying to understand the true nature of the child's power.
It's possible that the main character is the 'dark child' of course. There could also be a mentor - like figure, maybe an older wizard who tries to guide the child towards the light. And it wouldn't be surprising if there were some antagonists as well, such as other dark wizards who want to use the child's power for their own evil purposes.
Hermione Granger might also be a central character. Her thirst for knowledge could lead her into situations where she is in the dark, like exploring a new area of magic that has many unknowns. As a child in Hogwarts, she might be trying to solve a mystery that no one else has been able to, and she has to start from a place of not knowing much, or being 'in the dark' so to speak.
It's difficult to determine exactly, but if the fanfiction focuses on the concept of the 'child of the green' being a new addition to the wizarding world, then that character would be central. There could also be other important characters like Draco Malfoy. Since Draco is from Slytherin, his path might cross with the 'child of the green' in interesting ways. And of course, we can't rule out the possibility of some magical creatures being significant characters in this fanfiction as well, like a magical snake or a forest - dwelling creature, considering the 'green' theme.
Obviously, the child is one of the main characters. There might also be some prison guards who play important roles, either as antagonists or those who gradually change their views towards the child. And perhaps some other inmates who interact with the child could also be considered main characters.
There might also be appearances by Harry Potter and his friends. Since it's a fanfiction related to the Harry Potter universe, they could play important roles, either as mentors to the Rose Child or as characters who are initially suspicious of the Rose Child but then come to understand them. Hermione, with her vast knowledge of magic, could be helping the Rose Child understand their powers better. Ron could be the one who provides some comic relief during tense situations involving the Rose Child.
In this fanfiction, the main characters could be quite diverse. Since it's about a 'dark heir', there would likely be a character who embodies this role. It could be a previously unheard - of character with a complex backstory related to a dark legacy. Harry Potter might be involved to oppose this dark heir or to try and understand their motives. His friends, like Hermione and Ron, could also be part of the story. Additionally, there could be other magical beings or characters from the 'Harry Potter' lore, such as members of the Order of the Phoenix or Death Eaters, who are drawn into the plot due to the emergence of the dark heir.
Obviously, the Dark One is a main character. Harry Potter himself also often plays a crucial role as he is usually the one who has to face the Dark One in some way.
Well, Harry Potter is most likely one of the main characters as it's a Harry Potter fanfiction. He would probably be at the center of the new revelations and story developments.
There could also be an original character created specifically for this fanfiction who becomes the Dark Phoenix. This character would then be a central focus, with their transformation and the resulting events driving the story forward. Their backstory, motives, and relationships with other characters would be important aspects of the narrative.
I'm sorry, without reading the fanfiction it's hard to say for sure. But it could be an original character created for this story, along with some well - known Harry Potter characters like Harry, Hermione, or Ron who interact with this new character.
Since it's about Harry Potter being death's child, he is the central figure. However, Dumbledore could also be a significant character as he was always guiding Harry in the original series and might have some knowledge about this new aspect of Harry. Additionally, Voldemort could be an important character too, as his relationship with Harry was always about life and death, and this new concept in the fanfiction could change their dynamic.