Harry is surely the central character in 'harry trained as a pet fanfiction'. Besides him, it could be that his friends like Ron and Hermione are also involved, either trying to rescue him from this strange situation or being part of the process that led to his being trained as a pet. There might also be a new character, perhaps a dark wizard or a quirky magical creature, who is responsible for the training.
The main character is Harry. However, depending on the direction of the fanfiction, there could be other important characters. For instance, if it's set in Hogwarts, professors might play a role. They could be trying to figure out what's wrong with Harry or be in on the secret of his training as a pet. Also, there could be some sort of magical pet trainer character who has their own motives for training Harry in such a way, whether it's for power, revenge, or some other reason.
Obviously, Harry and Sirius are the main characters. Harry, the protagonist of the Harry Potter series, and Sirius, his godfather.
Obviously, Harry and Merlin are the main characters. Harry, the young wizard from Hogwarts, and Merlin, the legendary wizard from the past.
The main characters would be Harry Potter and Batman. Harry Potter, the young wizard from the wizarding world, is the focus as he is being trained. Batman, the Dark Knight from Gotham, brings his skills and knowledge to the table. There might also be some appearances from other characters in the Harry Potter universe, like Hermione and Ron, who could react to Harry's new training. And in the Batman side, perhaps Alfred could also play a role, providing support or advice in the training process.
The main characters are Harry Potter and Thor. But it's possible that some other important characters from both universes could play a role. In the Harry Potter universe, Dumbledore might have an opinion on Harry's new training. And in the Thor universe, Odin could be aware of Thor training an outsider like Harry. Their reactions and interactions could add more depth to the story in this fanfiction.
Obviously, Harry and Merlin are the main characters. Harry is the one being trained, and Merlin is the trainer.
I'm not sure specifically as there could be many different plots in such a fanfiction. It might involve Harry being magically or otherwise trained to behave like a pet, perhaps with some humorous or strange situations along the way.
Obviously, Harry Potter and Flitwick are the main ones. Harry as the student being trained and Flitwick as the trainer.
Obviously, Harry Potter would be one of the main characters. And then, there would probably be some members of the SAS. They could be tough, experienced soldiers who take on the task of training Harry.
Death, of course, would be a major character as it's training Harry. Maybe Dumbledore could also play an important role. He might be the one who initially guides Harry to this encounter with Death or acts as a moral compass during the training.
Perhaps there's a mentor figure, an old and experienced pet trainer who gives Harry advice from time to time. Another possible character could be Harry's rival in the pet training world. This rival might always be trying to outdo Harry in training different pets, which adds some drama to the story.