It could be Harry Potter himself, of course. He might be on a mission to either free someone wrongly imprisoned in Caer Azkaban or to stop a new dark threat emerging from there. Hermione could also be a main character, using her intelligence to figure out the mysteries of Caer Azkaban.
One interesting aspect could be how the magic system is tweaked in the fanfic. Since Caer Azkaban is such a dark and foreboding place, the magic used there might have different properties. Characters might have to adapt their magic in order to survive or escape. There could also be a sub - plot about a character trying to reform the prison system in Caer Azkaban, bringing in new ideas and magic to make it less of a hell - hole.
Dumbledore might play an important role as well. He would be guiding Harry through this new and strange situation. He could have some secrets about the Lord of Azkaban that he reveals to Harry over time. Also, some of the Azkaban guards or prisoners could become significant characters as Harry tries to reshape Azkaban.
Harry Potter himself is of course very common. He's usually the central figure in these fanfictions. Hermione Granger is also often included as she is Harry's friend and a brilliant witch. Ron Weasley too, as he's part of the trio. Sirius Black might also be a common character since he has a connection to Azkaban.
In the fanfic, there might be changes in the security measures of Azkaban. For example, new spells or wards could be added to prevent prisoners from escaping more effectively.
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 could also be new characters introduced specifically for this fanfiction. Maybe there's a vampire hunter who comes to Hogwarts thinking the vampire is a threat. This character would add a new layer of conflict and intrigue. Additionally, the teachers at Hogwarts, like Dumbledore, would still play significant roles as they try to maintain order in the school while dealing with this new and rather unusual situation.
Perhaps Hermione could be one of the main characters. Given her intelligence and knowledge of magic, she might be the one to figure out how to deal with the strange 'Lord of the Wind' magic that has entered the wizarding world. She could be researching ancient spells and texts to find a solution.
Obviously, Harry Potter himself is a main character. Since he is becoming Lord Potter, he is at the center of the story. Hermione and Ron are likely to be important characters as well, as they are Harry's closest friends and will surely be involved in his new journey as Lord Potter.
Some fanfics introduce a new character, a seer who can see not just the future but also alternate timelines. This character is unique as they can provide insights that no one else can, and often their visions drive the plot forward in unexpected ways.
The main characters in the 'Harry Potter Prisoner of Azkaban' full story include Harry Potter, a young wizard who is facing new challenges in his third year at Hogwarts. Ron Weasley, his red - haired and humorous best friend, and Hermione Granger, the intelligent and studious one. Sirius Black, an escaped prisoner from Azkaban with a mysterious connection to Harry. Professor Lupin, who has his own secrets related to being a werewolf. These characters interact in a world filled with magic, mystery, and danger. Their relationships and actions drive the plot forward, from the fear of Sirius Black to the revelations about his true identity and the use of time - turners to change the course of events.