One possible plot could be that Harry is wrongly accused of a serious crime within the wizarding world and is sent to Azkaban. There, he discovers a dark secret about the prison itself, like there being a hidden force controlling the Dementors. He has to use his skills and the loyalty of his friends to expose this secret and clear his name.
One possible plot could be that Hermione is wrongly accused of a serious crime against the wizarding world, perhaps a dark magic related offense that she didn't commit. As a result, she is sent to Azkaban. Inside Azkaban, she has to deal with the Dementors and the harsh prison environment. Meanwhile, her friends Harry and Ron believe in her innocence and start to investigate to find the real culprit and clear her name.
In this fanfiction, perhaps Harry goes to Azkaban to rescue someone. It could be a fellow wizard who has been unjustly imprisoned. He might have to use his skills and some new-found magic to navigate the dangerous and dreary corridors of Azkaban, all while avoiding the Dementors.
One possible plot could be that Harry is framed for a serious crime he didn't commit. Maybe someone has used Polyjuice Potion to look like him while doing dark magic. The wizarding community, believing the false evidence, sends him to Azkaban. In Azkaban, he has to endure the Dementors and try to prove his innocence from within the prison walls.
It could be a corrupted prison guard. They might be taking advantage of the chaos in Azkaban to carry out their own evil plans, like stealing magic from the prisoners. Harry would have to stop them while also dealing with his own situation in the prison.
One possible plot could be that Hermione discovers a dark secret about Azkaban. And the Ministry of Magic, fearing she'll expose it, sends her there. In Azkaban, she meets some other wrongly imprisoned witches and wizards. Together, they plan an escape while also trying to expose the real criminals in the wizarding world.
Well, perhaps Harry could discover the unique flora and fauna on Pandora. He might meet the Na'vi and learn their ways, like how to ride a banshee. And he could use his magic in unexpected ways in Pandora's environment.
Well, he might discover a hidden magical realm filled with strange creatures. Maybe he stumbles upon a lost spell that he has to master to get out of this new place.
Maybe it could be about Harry experiencing the Beltane festival. He might encounter magical creatures specific to Beltane, like enchanted fire sprites. He could also participate in the traditional Beltane celebrations such as the maypole dance and bonfire lighting, and along the way, he might learn about the significance of Beltane in the wizarding world.
Well, perhaps Harry is tired of all the chaos in the wizarding world. Maybe he decides to go on strike against the Ministry's unfair rules. He could be striking for better treatment of house - elves or more equality among wizards of different blood status.
Well, one possible plot could be that Harry goes to Durmstrang to learn different kinds of magic not taught at Hogwarts. Maybe he discovers a new form of defensive magic there. He could also make new friends who have different views on magic compared to his Hogwarts pals. And perhaps he gets involved in a mystery that is unique to Durmstrang, like an ancient curse on the school or a hidden artifact.