One interesting plot development could be the exploration of Harry's relationship with Sirius Black outside of prison. Maybe they go on adventures together, hunting down remaining Death Eaters. Another could be Harry's improved skills in Defense Against the Dark Arts, as he now has Sirius as a more regular mentor. And perhaps there are new magical creatures introduced that Harry and his friends encounter during their post - Azkaban adventures.
Some fanfictions might focus on the changes in Hogwarts after Azkaban. With Sirius being free and the threat of Voldemort still lingering, there could be more security measures put in place. Harry and his friends could be involved in uncovering secrets about these new security arrangements. There could also be new clubs or organizations formed at Hogwarts in response to the changing times. For instance, a club dedicated to protecting the school from the inside, which Harry and his friends would be key members of.
One idea could be exploring what would happen if Sirius Black was actually innocent but had a different, more complex plan than just escaping. For example, he might be trying to uncover a deeper conspiracy within the wizarding world that ties to his imprisonment.
In this fanfiction, perhaps a major plot point is Harry using his new position to reform Azkaban. He could introduce new ways of dealing with prisoners that are more humane. Also, his power might attract the attention of dark forces who want to either use him or destroy him, which would add a lot of action and suspense to the story.
One idea could be that Harry discovers a hidden magic within Azkaban that allows him to free wrongly imprisoned witches and wizards. He then uses this to his advantage to reform the wizarding prison system.
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 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.
One idea could be exploring Harry's journey in Azkaban in more depth, like how he copes with the dark and gloomy atmosphere. Maybe he discovers some long - forgotten secrets within the prison walls.
One interesting plot could be Harry struggling to fit in with the Slytherin ideals at first. He might be constantly at odds with some of the more traditional Slytherin values like pure - blood supremacy. But then he could gradually change the house from within, making his Slytherin peers see that not all Gryffindor traits are bad and vice versa.
In some of these fanfictions, Harry might gain god - like powers and use them to reshape the wizarding world. For example, he could end all forms of dark magic at once. Maybe he uses his newfound divinity to bring back lost loved ones, like his parents, in a way that doesn't disrupt the natural order too much.
In some of these fanfictions, Harry might start exploring the dark art of necromancy secretly. He could be driven by a desire to bring back his lost loved ones, like his parents. This often leads to him having to hide his newfound interest from his friends at Hogwarts, creating a lot of internal conflict as he struggles between what he knows is right and his longing for his family.
One interesting plot development can be that Harry levels up his Occlumency skills to an extraordinary level. This would mean he can not only block Voldemort from invading his mind but also be able to read the minds of others to some extent. This would give him a huge advantage in battles and in uncovering mysteries. For instance, he could use this skill to figure out the true intentions of some of the more ambiguous characters in the wizarding world, like Snape. And it would completely change the dynamics of his relationship with other characters, as they would be more cautious around him knowing he can peek into their thoughts.