Neville would likely be one of the first to join. He has always been brave and has a strong sense of justice. Luna Lovegood might also be part of it. Her unique perspective and knowledge of the wizarding world could be very useful. And then there are the Weasley twins. Their skills in magic and their ability to think outside the box would make them great assets.
In such a fanfiction, Harry might start by gathering students who feel marginalized or unheard in Hogwarts. He could be motivated by the inefficiency of the existing school authorities in dealing with the growing dark threats. He'd probably use his own skills and knowledge to train them, just like he was trained in Dumbledore's Army. Maybe he'd include students from all houses, uniting them under a common cause of protecting the wizarding world.
Perhaps he barters with magical beings. He could offer his services in solving magical problems for them in exchange for rare building resources. For example, he might help a group of centaurs with a prophecy issue and in return, they give him enchanted wood or special stones. He may also get help from his friends who have access to different resources. Hermione might provide some rare books with building spells, and Ron could get some things from his family's old collection.
First, think about the characters you want to include in your 'Harry Potter Army'. Decide if you're going to use the original members from Dumbledore's Army or introduce new ones. Then, come up with a unique plot. It could be something like the army has to face a new dark wizard that the original books didn't cover.
Obviously, his friends Ron and Hermione would be among the first to join. Neville could also be a key member, as he has shown great courage. Then there might be the members of Dumbledore's Army who are still at Hogwarts. The Weasley twins could also be part of it, using their unique magical inventions to give the army an edge in battle.
In fanfiction, Harry Potter might create his own magic through intense study of ancient and forgotten magical texts. He could discover long - lost incantations and then modify them to suit his needs. Also, his unique connection to Voldemort could play a role. By understanding the dark magic within Voldemort and combining it with the positive magic he's learned, he could create a new form of magic that balances both light and dark elements.
In Harry Potter fanfiction, a character being 'his own man' might mean that he has the independence to make his own choices, regardless of the expectations of others. For example, a character might not follow the typical path set by the original story, like a Slytherin who decides to oppose the pure - blood supremacist views of his family.
Harry might first decide on the values of his world. Is it a world that values equality above all? Based on that, he'd then start to create institutions. He could build a magical council that enforces these values. He would also need to think about the inhabitants. Would he populate it with new species or just bring in his old friends? He could use his creativity to design unique magical creatures that are different from those in the original Potter world. And of course, he'd have to establish a system of magic that is distinct yet still related to what he already knows.
It means that Harry Potter's character continues to exist and develop in the world created by fanfiction writers. Fanfiction allows fans to explore different scenarios and storylines for Harry that may not be in the original books or movies.