One idea could be Hermione discovering a hidden spell in the Prisoner of Azkaban events that helps her protect Harry in a more unique way. For example, a spell that can temporarily freeze time around a small area, allowing them to escape from danger more easily.
One idea could be that Ron and Hermione accidentally stumble upon a secret passage in Hogwarts while investigating the mystery of the Prisoner of Azkaban. This passage could lead them to a hidden chamber where they find clues about Sirius Black that no one else has discovered yet.
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.
One possible plot could be that Hermione was wrongly accused of a serious crime against the wizarding world. Maybe she was framed by a dark wizard who wanted to silence her for her intelligence and knowledge. She might be struggling to prove her innocence from within Azkaban while her friends on the outside, like Harry and Ron, are desperately trying to find evidence to free her.
One idea could be exploring Sirius Black's life more in depth during his time on the run. Maybe he had some secret encounters with other magical creatures that he never told Harry about.
Maybe in the fanfiction, Hermione gets accidentally sent back in time instead of Harry when they are trying to save Sirius. She then has to use her wits to find a way to not only save Sirius but also to get back to her own time, which adds a whole new layer of complexity to the story.
One idea could be exploring Sirius Black's time on the run in more detail. Maybe he had some secret encounters with other magical creatures that he didn't tell Harry about. Another could be a story from the perspective of Remus Lupin during his time as a teacher at Hogwarts that year, and how he was constantly worried about his werewolf secret being exposed while also trying to protect Harry. A third idea could be a fanfic that focuses on Hermione's time - turning device, and what would happen if she accidentally sent herself back too far in time and had to find a way to get back to the right time without disrupting the timeline too much.
One interesting theme is the power of friendship. In the 'Prisoner of Azkaban' setting, Harry and Hermione already have a strong bond. Fanfictions often explore how this bond can be deepened and transformed. For example, they might face challenges together that make them realize their feelings for each other are more than just friendship.
A cool plot twist might be that the time - turner Hermione uses has some unforeseen side effects. Instead of just allowing her to attend more classes, it starts to create glitches in time that cause different events from the past to bleed into the present. For instance, old spells from the founders of Hogwarts start to randomly appear in the corridors, and the characters have to figure out how to stop this chaos while also dealing with the Sirius Black situation.
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.
A possible plot twist is that Ginny has a premonition about the real threat in the 'Prisoner of Azkaban' situation. It's not actually Sirius Black as everyone believes, but a dark wizard who has been using the Sirius situation as a distraction. Ginny then teams up with Harry to expose the truth, and in the process, their bond grows stronger.