Obviously, Harry and Sirius are the main characters. Harry is the one trying to break Sirius out, and Sirius is the one being broken out.
In this fanfic, Harry is the main focus as he's the one sent to Azkaban. However, other characters would also be important. The guards at Azkaban, the Dementors, would be key figures as they would be the ones constantly menacing Harry. Then there are the Ministry of Magic officials who were involved in sending Harry there. Their motives and actions would be crucial elements in the story.
Obviously, Harry Potter himself would be a main character. He would be at the center of any story that involves 'Harry Potter rules Azkaban' as he is the one who is supposed to 'rule' in some way.
One interesting plot point could be how Harry devises the plan to break Sirius out. Maybe he uses his invisibility cloak and some clever spells. Another could be the reactions of the other characters when they find out, like Hermione's concerns about the legality and consequences.
Obviously, Harry Potter himself is a main character. Hermione and Ron often play important roles too. They might try to break Harry out of Azkaban or help him from the outside. Sometimes, Sirius Black could also be involved, especially if the story is related to the secrets of Azkaban or the wrong imprisonments. Dumbledore could also be a key figure, guiding Harry or influencing the events from afar.
Well, obviously Ruby herself. Then there's her teammates Weiss, Blake, and Yang. Depending on the nature of the relationship in the fanfiction, Yang might be deeply affected if it's a family - like bond that's breaking. Weiss could be involved in trying to mediate or give her two cents on the situation from her logical perspective.
Obviously, Harry Potter himself is the central character. Hermione and Ron would most likely be involved too. They would probably try to find a way to get Harry out of Azkaban. Dumbledore might also play a role, perhaps guiding Hermione and Ron from behind the scenes or even trying to influence the wizarding court to re - evaluate Harry's case.
Obviously, Harry Potter himself is the central character. But often, his friends like Hermione and Ron may also be involved as they are closely associated with him in the original series.
In addition to the ones mentioned, Dumbledore could be a character in the fanfiction. He might try to temper Sirius's thirst for revenge and guide him towards a more just path. On the enemy side, Peter Pettigrew would be a central figure. Since he was the one who really betrayed James and framed Sirius, Sirius would likely be out for revenge against him. And Bellatrix Lestrange, as a prominent Death Eater, would also be a likely target for Sirius's revenge.
Obviously, Harry himself would be the main character. His friends like Ron and Hermione are also likely to be involved. They would probably try to support Harry or figure out what's going on with him.
Maybe he uses some powerful magic spells that he has learned secretly. For example, the Patronus charm could be used to fend off the Dementors which are the main guards in Azkaban. He might also get some unexpected help from his friends or some mysterious characters within the fanfiction world.