Obviously, Harry is one of the main characters. There might also be some of his friends like Hermione and Ron who could get involved with the story related to the breeding grounds.
There could also be some of the teachers or staff from Hogwarts in the 'breeding grounds hp fanfic'. For example, Hagrid would be a very likely character to be involved, given his love and knowledge of magical creatures. His presence could add a sense of authenticity and guidance in the breeding ground scenarios.
One interesting plot could be the discovery of new magical creatures in the breeding grounds. Maybe Harry stumbles upon a rare species that has been thought extinct. Another could be the breeding grounds being in danger and Harry has to use his skills to protect it.
Obviously, Harry and Lily are the main characters.
I'm not sure specifically who the main characters are in 'the breeding ground fanfiction' as it can vary greatly depending on the writer's vision. It could be a group of scientists studying the breeding ground if it's a science - based fanfiction.
Often, in Pokemon breeding center fanfiction, there are trainers who bring their Pokemon to the center. So, these trainers can be main characters as they interact with the breeders and their Pokemon. There might also be a head breeder who manages the whole center and makes important decisions regarding the breeding programs.
In a 'breeding grounds fanfic', you might consider writing about the different seasons in the breeding grounds. How do the inhabitants adapt? What new life is born during each season? You could also introduce a new character who has a special connection to the breeding grounds, like they can communicate with the animals there or understand the language of the plants.
Hagrid is often a central character in 'Harry Potter breeding creatures fanfiction' as he has a great love for magical creatures. He might be involved in breeding projects, using his extensive knowledge. Another popular character could be Newt Scamander. Given his expertise in magical beasts, he could be a mentor or even directly involved in breeding rare or endangered creatures in fanfiction stories.
Often, the daughters of Naruto, Sasuke, and other main characters from the original Naruto series are the main characters. For example, Naruto's daughter might inherit his determination and his unique jutsu, and she would be central to the story, facing challenges in the ninja world.
One interesting aspect could be the unique magical creatures that might be introduced in the 'breeding grounds' setting. It could expand on the already rich fauna of the Harry Potter universe.
First, do some research on the concept of breeding grounds if it's based on a specific world or lore. Then, think of a main character or a group of characters. For example, you could start with a young adventurer who stumbles upon the breeding grounds.