One interesting aspect could be how the magic system is tweaked in the fanfic. Since Caer Azkaban is such a dark and foreboding place, the magic used there might have different properties. Characters might have to adapt their magic in order to survive or escape. There could also be a sub - plot about a character trying to reform the prison system in Caer Azkaban, bringing in new ideas and magic to make it less of a hell - hole.
It could be Harry Potter himself, of course. He might be on a mission to either free someone wrongly imprisoned in Caer Azkaban or to stop a new dark threat emerging from there. Hermione could also be a main character, using her intelligence to figure out the mysteries of Caer Azkaban.
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 interesting plot point could be that Hermione tries to teach the Marauders' Map to sing. Imagine the map singing out the locations of people in a really off - key voice. It's a hilarious take on the magical item. Also, perhaps Sirius Black disguises himself as a fluffy bunny to avoid detection at Hogwarts, which is completely different from his usual menacing image in the original 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 plot twist could be that Sirius Black is actually being framed by a more powerful dark wizard who has the ability to disguise as others. This would add an extra layer of mystery.
In some fanfics, Lupin might turn out to be under the influence of a spell that makes him seem more dangerous than he actually is. Maybe the real threat is a hidden character who is using Lupin's condition to create chaos. For example, they could be making him lose control of his werewolf form more often than normal, which would lead Harry and his friends to suspect Lupin wrongly.
In the fanfic, there might be changes in the security measures of Azkaban. For example, new spells or wards could be added to prevent prisoners from escaping more effectively.
One interesting plot point is the clash of cultures. Sasuke, coming from a world of ninjas, has a very different upbringing and set of values compared to the wizards in Harry Potter. For example, his idea of combat and self - defense is more physical and stealth - based, while the wizards rely on spells. When these two meet, it creates a lot of interesting situations where they have to learn from each other.
A common interesting plot point is Itachi's Sharingan in the wizarding world. It gives him an edge that no one in the wizarding world has seen before. For example, in some fanfics, he can use it to see through magic spells and illusions that even the most powerful wizards can't detect easily.
The concept of free will is often explored in a unique way. In the Harry Potter universe, characters have their own destinies influenced by magic and prophecy. In Westworld, the hosts are starting to discover their free will. When combined in fanfic, it can lead to really thought - provoking scenarios where characters from both universes question what it means to be truly free.