One interesting plot is when Harry discovers a hidden prophecy about Sirius Black that leads him on a dangerous quest to uncover the truth. Another is when Harry suspects Sirius of being involved in a dark magic plot and has to spy on him secretly. There are also stories where Harry and Sirius team up to investigate an ancient mystery within the wizarding world that has been long forgotten.
Another aspect of this fanfiction could be that Harry uses his Parseltongue ability to communicate with the snakes in Azkaban (if there are any). The snakes might have some information about Sirius since they can sense the emotions and secrets of the prisoners. Through this unique method, Harry gets closer to proving Sirius's innocence.
Harry could also team up with Hermione and Ron. Hermione would use her extensive research skills to dig into the Ministry's files on Sirius. They might find that there were some irregularities in the trial process. For example, crucial evidence was withheld or fabricated. Ron, on the other hand, could use his family's connections within the wizarding world to gather more information about the people who were involved in the case against Sirius.
You can start by looking on popular fanfiction websites like Fanfiction.net or Archive of Our Own (AO3). On Fanfiction.net, use the search bar and type in 'Harry investigates Sirius Black'. Sort the results by popularity or rating to find the well - liked ones. AO3 also has a great search function. You might also want to check out some Harry Potter - focused fan communities on platforms like Reddit, where fans often recommend their favorite fanfictions.
Well, in some of these fics, Sirius might time - travel to save Harry from a future threat. For example, he could see a vision of Harry being killed by Voldemort in a new and terrifying way, and then he uses time - turning magic to go back and change the course of events.
Well, one possible plot could be Sirius seeking revenge on the Death Eaters who wronged him. He might use his Animagus form to spy on them and then plan elaborate traps. Another could be his revenge on those who framed him for the crimes he didn't commit, like using his intelligence to expose their lies in a very public and embarrassing way.
In some fanfictions, the Whomping Willow might be a sentient being that has a special connection with Sirius Black. Maybe it was enchanted by a powerful wizard long ago, and only Sirius, with his unique magical aura, can communicate with it. This could lead to a plot where Sirius enlists the help of the Whomping Willow to defeat a common enemy, like a group of dark wizards who are after Hogwarts.
Another interesting plot could be that when Hermione travels back, she finds that Sirius has a much different personality than she expected. Maybe he's more cunning or more vulnerable. This changes the dynamic between them and leads to a more complex and emotional story. The author can then explore how Hermione adapts to this new version of Sirius and how they work together to face the challenges in the past.
One interesting plot could be that Harry and Hermione discover a hidden time - turning spell. They use it to go back in time just enough to prevent Sirius from being framed in the first place. So they gather evidence of Peter Pettigrew's true nature before he can shift the blame onto Sirius.
One interesting plot could be Harry, now as Orion Black, using his knowledge from his previous life to change the fate of the Black family. He might try to prevent some of the dark deeds the family was involved in. Another could be his interactions with the younger versions of characters he knew before, like Snape or Sirius. It would be really fascinating to see how he navigates the wizarding world with this new identity and old memories.
One common plotline is Sirius Black escaping from Azkaban earlier and secretly training Harry in advanced magic. Another could be Sirius and Harry going on a hidden adventure to uncover more about Harry's parents. There are also stories where Sirius plays a more active role in the fight against Voldemort at Hogwarts, using his knowledge of the Dark Arts and his Animagus form to their advantage.