Professor McGonagall could play a significant role as well. Since she is an animagus herself, she could be Harry's mentor in this process. She might teach him how to control his form, give him advice on the ethics of using his animagus ability, and share her own experiences as an animagus.
Hermione would also be important. She would likely be researching alongside Harry, helping him with the theory and knowledge behind becoming an animagus. Maybe she even discovers some rare spells or potions that can aid Harry in his transformation.
Another possibility is that he becomes a fox. Foxes are clever and sly, which are qualities that Harry has developed over the years. As a fox, he could use his wits to outsmart his opponents. He could also easily blend into the forest environment, which would be handy for hiding or sneaking around.
In 'harry becomes lord potter at 7 fanfiction', Harry is the main character, but there could be other important characters too. Maybe there are some members of the Potter family's old allies who come forward to help Harry. For example, the Longbottoms could be important as they have a long - standing relationship with the Potters. And then there might be some antagonists, like the Malfoys, who could be envious or try to undermine Harry because of his new title.
In this fanfiction, it could be that some of the Slytherin students who side with Voldemort become the main antagonists. They might be jealous of Harry's new power and try to expose him or cause trouble for him. For example, they could set traps in the forest hoping to catch Harry when he's in his deer form.
Hermione could be important. She might help Harry with his studies, providing him with books and research materials on healing magic. Also, Ron could be there, perhaps he gets injured a lot in his new job and Harry has to keep patching him up. And then there could be the head healer at St. Mungo's who acts as Harry's mentor, guiding him through the complex world of healing.
Hermione is often paired with Harry. She might help him study and understand the animagus transformation better. Also, Ron could be there, providing his usual comical relief and loyalty. They could get into all sorts of adventures together with Harry as an animagus.
Minerva McGonagall is also a favorite. Her Animagus form of a cat gives a lot of room for creativity. Fanfictions might show her observing Hogwarts in her cat form, seeing things that she wouldn't as a human, and using that knowledge to protect the school and its students.
Obviously, Harry Potter is one of the main characters since it's in the title. He is the one with the animagus ability in this fanfiction.
Well, Harry is central of course. But in many fanfictions, Sirius Black might also be an important character. Since he is an animagus himself, he could be a mentor to Harry in his dog form. Then there are the villains. Voldemort or his Death Eaters could be involved as Harry's dog animagus form might be used to thwart their plans. And Neville could also be in the story, perhaps being a bit confused or intrigued by Harry's new form.
Ron Weasley could also be a main character. His loyalty to Harry would make him involved in the story. He might be there to support Harry, or perhaps even be a bit jealous of Harry's new ability at first but then come to terms with it and help Harry use it to their advantage in their adventures or against their enemies.
Well, it's highly likely that there is. The Harry Potter fanfic community is vast and full of diverse ideas. Writers often explore unique combinations like this. In such a fanfic, perhaps Harry's Animagus form could have features similar to a basilisk, like the deadly stare or the ability to move through small spaces like a snake. He might also face challenges or advantages based on this form in the story, which could make for a very interesting read. You should start your search on popular fanfic sites and see if you can uncover this kind of gem.