A new character could be the main character. A young witch or wizard from a far - off land who comes to Hogwarts with a mysterious past. They find that they need to hide as a pet to adapt to the new and often intimidating environment of Hogwarts. As a pet, they observe the other students and learn about the different houses and the unique culture of Hogwarts, all while trying to keep their true identity a secret.
It could be a young wizard who is an outcast in the wizarding world. Maybe they have some unique powers that others fear, so they choose to hide as a pet to avoid persecution.
Well, it could be about a character who is forced to hide their true identity and pretends to be a pet in the wizarding world. Maybe they are on the run from some dark wizards and find a safe haven by disguising as a pet in a Hogwarts dormitory.
Petunia Dursley could also be a main character. She is in charge of the household and the pet. In the fanfiction, we could explore how she views the pet and how her attitude towards the pet changes when strange things start to happen, perhaps due to Harry's influence or the pet's own mystery.
Perhaps an ancient evil that has been awakened by the presence of the pet dog in the wizarding world. This entity doesn't like the idea of a human - dog bond being so strong in a place full of magic. It starts causing chaos in Hogwarts and the surrounding areas, and Harry and his pet dog have to figure out how to stop it.
One main character could be a young, aspiring wizard who has always dreamed of having a magical pet. He visits the pet shop regularly to look at all the amazing creatures. Another could be the eccentric old owner of the pet shop who has a wealth of knowledge about magical pets.
Maybe it's an anonymous gift from someone who has been observing Harry. This person could be a former student of Hogwarts who has a special connection to snakes and sees that Harry has a kind heart and would take good care of the snake. So they leave the snake for Harry to find with a simple note that just says 'For Harry Potter'.
Maybe Professor McGonagall. She was strict but also had a soft spot for Harry. She might take Harry under her wing more in this fanfiction and make him her 'pet' student. She could teach him advanced Transfiguration skills or involve him in Gryffindor - related leadership tasks that give him an edge over the other students.
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.
A lesser - known character like Ernie Macmillan from Hufflepuff could be the main character. As a prefect, he could bring out the unique qualities of Hufflepuff house. He might have to deal with issues like other houses underestimating Hufflepuff students. His story could focus on how he promotes the values of hard work, loyalty, and fairness within the house and the school as a whole.
Hermione could be a great main character. She's curious and intelligent, so she would be really interested in exploring the secrets of the diary. She could use her vast knowledge of magic to try and figure out how the diary works and what secrets it holds.
Harry Potter himself could be the main character as a revenant. Maybe he has some unresolved issues from his past, like his relationship with his parents. His revenant form could be on a journey to fully understand their sacrifice and his own place in the wizarding world's history.