One common theme is injustice. Since Sirius was wrongly accused, fanfictions often explore how unfair the trial was. Another theme is loyalty, as his friends' loyalty to him is shown in different ways. For example, they might try to find evidence to clear his name.
The fanfiction could start with Sirius being magically transported to a new, more just courtroom. Dumbledore could be secretly working behind the scenes to ensure a fair trial. The trial could be full of twists and turns. For example, the dementors that were involved in his original imprisonment might be called as witnesses, but Sirius could use his knowledge of their weaknesses to discredit them. And in the end, he is proven innocent, much to the joy of his supporters and the shock of his enemies.
Well, I really like 'Sirius Black: The Trial Chronicles'. It does an amazing job of painting the scene of the trial, with detailed descriptions of the courtroom and the characters involved. It shows Sirius's determination and his relationships with others in the face of false accusations. Another interesting one is 'In Defense of Sirius', where the author imagines different ways the trial could have gone if Sirius had better legal representation. And 'The Trial of Sirius Black: A Different Perspective' offers a fresh view on the events leading up to and during the trial.
Obviously, Sirius Black himself is a key character. He's the one on trial, so he'll be at the center of the story. Then there's Harry Potter. He might be very involved, trying to prove Sirius's innocence. Hermione Granger could also be important, using her research skills to dig up evidence. And Remus Lupin, as Sirius's old friend, would be a crucial witness.
Hermione would definitely be a great help. She's smart and resourceful, and could do a lot of research to find evidence. Also, Ron would be there, providing support and loyalty as always.
In such a fanfiction, perhaps Harry discovers some new evidence that was overlooked. He might find a witness who was too afraid to come forward before. Then he presents this evidence to the Ministry, forcing them to give Sirius a trial.
Well, Sirius might face a series of challenges during the trial. He could be wrongly accused and have to fight hard to prove his innocence. Maybe his friends would come to his aid, bringing new evidence or testifying on his behalf.
Obviously, Sirius himself is the central figure. His friends like Harry, Hermione, and Ron could be involved. They might be in the courtroom, trying to support Sirius in any way they can. The Ministry of Magic officials would also be there, as they are the ones conducting the trial.
Some independent fanfiction blogs also host such stories. However, they can be a bit harder to find. You can start by searching for Harry Potter fanfiction blogs through search engines. When you find some, check if they have a search function on the blog itself and look for the 'harry gets sirius a trial' fanfiction there.
Well, in these fanfictions, we see a more vulnerable side of Sirius. For example, in many of them, his time in Azkaban is explored in greater detail. We get to understand the true extent of the psychological damage it caused him, which makes his character more three - dimensional.