Remus Lupin is often present. He was one of Sirius' old friends and a fellow Marauder. Their friendship can be delved into deeper, especially considering the complex history between them. Dumbledore is another common character. He plays an important role in the wizarding world and his interactions with Sirius can add depth to the story.
In some 'sirius black after azkaban fanfiction', there could be a plotline where Sirius has to deal with the stigma of being an escaped convict, even though he was wrongly imprisoned. He might face distrust from some in the wizarding community. At the same time, he could be on a journey to find out who really betrayed his friends all those years ago, which leads him on an adventure full of mystery and danger.
One could also write a fanfiction about Sirius Black's impact on Hogwarts during the events of Prisoner of Azkaban. For instance, his presence, even though he's on the run, could have a big influence on the students. Some students might start to question the Ministry of Magic's actions, and Sirius could inspire them to fight for justice.
In many fanfictions about Sirius Black in Prisoner of Azkaban, he is often given a chance for a new adventure. Writers might imagine him escaping Azkaban in more elaborate ways, or having different interactions with Harry Potter and his friends. For example, some fanfictions have him forming a secret alliance with other prisoners to break out together.
One great fanfiction could be 'Sirius's Redemption'. In this fic, Sirius, after escaping from Azkaban, tries to reintegrate into the wizarding world while dealing with his past traumas. It delves deep into his relationships with Harry and his old friends. The author does an amazing job of portraying Sirius's struggle with his sanity after years in that dark prison. Another interesting one is 'Sirius: A New Beginning'. It focuses on Sirius starting a new life outside of the shadow of Azkaban, exploring new magic and forming new alliances. It's a really engaging read if you like seeing the character grow in different directions.
One idea could be that Sirius Black's daughter, who has been hidden away all this time, discovers her true identity while trying to break into Azkaban to clear her father's name. She could have some unique magical abilities that help her in this dangerous quest.
A good Sirius Black post - Azkaban fanfiction should first of all capture his character accurately. He has been through a great deal in Azkaban, so his mental state should be reflected realistically. For example, his paranoia and his moments of confusion. Also, the relationship with other characters like Harry, Hermione and Ron is crucial. If it's a story where he tries to be a part of Harry's life again, it should show the complexity of that relationship. Good use of the wizarding world's lore is also important. Maybe he discovers some old magic related to his family while trying to start anew. And, of course, an engaging plot that keeps the readers hooked from start to finish.
She could be seeking revenge against those who wronged her father. So she goes to Azkaban, using her father's old contacts and knowledge, to find the real culprits. She might be a powerful witch, with skills in Occlumency to protect her mind from the dark influences in Azkaban.
Bellatrix Lestrange could be a great addition. Her extreme loyalty to Voldemort and her relationship with Narcissa as sisters, and her hatred for Sirius as a blood traitor, would add a lot of tension to the story.
The theme of freedom is quite important too. Sirius was locked up in Azkaban for a long time, and when he escaped, he was fighting for his freedom. Fanfictions often expand on this, showing his journey to fully regain his freedom and his place in the wizarding world, while also dealing with the prejudice against him because of his supposed crimes.
The theme of redemption also shows up. Since Sirius had a somewhat 'tainted' reputation in the eyes of the Black family, some fanfictions explore if Orion could have played a role in his redemption or if Sirius could have redeemed the family name in Orion's eyes.