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.
Well, Harry Potter would probably become an even more powerful wizard. Thor's combat skills and physical strength could be incorporated into Harry's magical abilities. Maybe he'd be able to cast spells while doing some of Thor's epic leaps and strikes.
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.
He might become more bold. Thor is a very bold character, and his influence could make Harry less hesitant.
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.
In this fanfiction, Harry Potter trained by Thor could lead to some interesting character development for Harry. Thor's brash and confident personality might influence Harry to be more assertive. Harry could also learn about different forms of power from Thor, not just magic. He might gain a new perspective on heroism and leadership. And who knows, maybe they would go on quests together that are completely different from what Harry has experienced in the wizarding world.
Obviously, Harry Potter and Godric Gryffindor. There might also be some other Hogwarts founders making cameo appearances.
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.
Obviously, Harry and Sirius are the main characters. Harry, the protagonist of the Harry Potter series, and Sirius, his godfather.