Well, you could have a plot where a rare and dangerous pet escapes from the Pet Shop of Horrors and the main characters from Harry Potter have to track it down before it causes chaos in the wizarding world. Maybe there's a pet that can change its form and is being used by a dark wizard to spy on Hogwarts students. Or it could be that a special pet is the key to unlocking a hidden magic in the Forbidden Forest and different characters are vying to get it from the pet shop.
One idea could be exploring the backstory of the shop owner. Maybe he has a tragic past that led him to open this strange pet shop. Another could be a customer who gets a pet that changes their life in unexpected ways, like a small pet that actually helps them solve a big mystery in their town. Or perhaps a story about a group of friends who visit the pet shop together and each has a different encounter with the creepy pets.
One idea could be exploring the backstory of Audrey II more in - depth. Maybe it came from a far - off planet where plants have a different form of intelligence. Another could be a time - travel fanfic where a character goes back in time to stop the plant from ever being brought to the flower shop.
One idea could be Seymour exploring an alternate universe where Audrey II doesn't have a thirst for blood. He could live a normal life, running the flower shop peacefully. Another could be Seymour traveling back in time to prevent himself from ever finding Audrey II in the first place. This would change the entire course of events in the story.
Another interesting plot could be set in an alternate universe where the little shop of horrors is a well - known and legal establishment. The characters have to deal with the moral implications of running such a place that feeds on human flesh but is also a source of great power and wealth.
Harry Potter himself could be a main character. He might be on a mission to find a pet for a friend or to solve a mystery related to the pet shop. Hermione would also be a great choice as she's always interested in learning about new magical creatures. And Hagrid, of course, with his love for all beasts, could play a major role.
Perhaps in the fanfiction, Orin's love is a redemption arc. He meets a kind-hearted person who shows him what real love is. As he falls in love, he starts to change his ways, from being a bully to a more sympathetic character. This would be a great way to explore his character development in a new light.
A plot could be that Snape's pet is a phoenix, which is a very rare and powerful magical creature. Harry Potter is intrigued by this phoenix and tries to get closer to it. Snape is initially against this but as the story progresses, he sees that Harry has a pure heart and allows him to interact with the phoenix. This could lead to a bond forming between Harry and Snape through their shared interest in the phoenix.
One possible plot could be that a new, mysterious pet appears in the pet shop in Diagon Alley. This pet has some unique magical abilities that no one has ever seen before. A young witch or wizard discovers it and tries to figure out its origin and how to take care of it. Maybe it's a key to an ancient magic mystery.
One idea could be an OC who has a special power like being able to communicate with all the pets in the shop at once. This could lead to all kinds of adventures, like solving mysteries when the pets' toys go missing. Another plot could involve an OC who is a new pet in the shop and has to learn how to fit in with the other pets. Maybe they have a different species - like a magical unicorn - which makes it even more challenging.
One idea could be a story where a young wizard discovers a dragon egg in the Forbidden Forest. He decides to secretly hatch it and raise the dragon as his pet. As the dragon grows, he has to constantly hide it from the Hogwarts professors, especially Hagrid who has his own ideas about magical creatures.