Perhaps he retreats due to the losses he has endured. He has lost many friends and loved ones throughout his journey. This grief could lead him to seek solitude within his own self in fanfiction. Also, he may be trying to come to terms with his identity as both a wizard and a person with a unique destiny. Stepping back into his own self could be a way to reconcile these two aspects.
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.
A simple fanfic could have Tonks and Harry on a mission together. When Harry is about to be attacked, Tonks jumps in, yells'mine' to the attacker as a warning that Harry is under her protection, and then hugs Harry to make sure he's okay. This shows Tonks' loyalty and her fierce protectiveness over Harry.
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.
The original story has a very linear family structure and a set timeline of events. But in this fanfiction, the very foundation of Harry's existence is altered. It might change his relationships with other characters too. For example, his relationship with his mother would be extremely different as he is now in a position where he has to be the one to start the family with her. His role in the wizarding world would also shift as he now has a very unique identity that defies the normal laws of nature. This could lead to new adventures and challenges that are completely different from what he faced in the original story.
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.