Yes, it's possible. Sirius is a popular character in the Harry Potter series, and many fans like to imagine him in different scenarios in fanfiction. He has a complex personality and a lot of untold stories, so fanfiction about him in the context of 'Prisoner of Azkaban' can be very interesting.
One common plot idea is exploring Sirius Black's life more in - depth. Maybe a fanfiction could focus on his time in Azkaban before his escape, showing his mental state and how he coped. Another idea is changing the roles. For instance, what if Hermione was the one who was wrongly accused instead of Sirius? It would create a whole new dynamic.
You can try some popular fanfiction websites like Fanfiction.net or Archive of Our Own (AO3). On Fanfiction.net, you can use the search bar and type in 'Prisoner of Azkaban' to get a list of relevant fanfictions. AO3 also has a great collection and advanced search options to help you narrow down to the exact type of fanfiction you're looking for based on tags such as characters, relationships, and genres.
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.
Sirius might be a bit angry if the fanfiction misrepresented him. He was a proud Gryffindor and a loyal friend. If the stories made him out to be something he wasn't, like a coward or a traitor in a different way than what was in the real story, he'd be offended. But on the other hand, if the fanfiction showed his true essence and added more depth to his relationships, he might be quite impressed.
You can start by looking on fanfiction websites like FanFiction.net or Archive of Our Own (AO3). These platforms have a wide variety of fanfictions related to 'Prisoner of Azkaban'. Just use the search function and type in relevant keywords like 'Prisoner of Azkaban' and 'Hogwarts' to find some great reads.
The 'Prisoner of Azkaban' has such a rich and complex plot, and fanfictions allow fans to explore different aspects of it. For example, they can delve deeper into the relationship between Harry and Sirius. In fanfiction, writers can create new scenarios and conversations that the original book might not have had time for.
The fanfics that expand on the relationship between Harry and his father's friends are also really good. In some, you can see how Remus Lupin might have tried to guide Harry in a more fatherly way, similar to how James Potter would have. They can be quite heartwarming and give a different perspective on Harry's growth at Hogwarts.
When it comes to Harry in these fanfictions, his relationship with his parents' past is often delved into in new ways. He might discover that his father had some unfinished business at Hogwarts that is now affecting the present. And this new discovery could change his perception of himself and his role in the wizarding world. In addition, Snape's character can be explored in a less antagonistic way. Fanfic writers may show his hidden motives for protecting Harry that go beyond his love for Lily. Maybe he has a grander plan to save the wizarding world that involves Harry in a more complex way.