Ron could also play a significant role. He might be torn between his loyalty to Harry and his family and the wizarding world. He could join Harry on his travels for a while, or he could stay behind but still be in contact with Harry, sending him care packages of wizarding treats and useful items.
Neville could be important too. He could take on a leadership role in the wizarding world in Harry's absence. He might be the one who continues to uphold the values that Harry fought for during the war. And when Harry returns (if he does), Neville could be the one to show him how the wizarding world has changed and grown in his absence.
Perhaps Harry meets magical creatures that are rarely seen by wizards. Since he is out exploring after the war, he might stumble upon a group of centaurs who have their own unique wisdom about magic and the future. He could also encounter veelas, and through his interactions with them, learn more about the different cultures within the magical world. There's also a chance he meets other young wizards who are on their own adventures, and they form a sort of traveling group together.
The hospital staff would surely be important. For example, a kind - hearted nurse who always takes care of Harry and becomes like a mother figure to him. There could also be an old doctor who has seen many strange cases and is intrigued by Harry's situation. Another character could be a fellow patient, a young girl who is also a wizard but has been hidden away in the hospital for a different reason. They could become friends and help each other through their difficult times in the hospital.
One possible storyline could be that Harry leaves to explore the wizarding world outside of Britain. He might go on a journey to discover new magical creatures and spells that were previously unknown to him. Maybe he wants to find a place where he can truly be at peace after all the chaos of the war.
A potential character could be a reclusive old wizard who lives on the outskirts of the wizarding world. This wizard might have his own reasons for living in seclusion, but when he sees Harry's loneliness, he takes him under his wing. Another character could be a young, orphaned witch who is also trying to find her place in the post - war wizarding world and she crosses paths with Harry.
One possibility is that Sirius, having finally been vindicated and after the chaos of the war, decides to travel the wizarding world to heal. He might visit old friends and places from his youth that he couldn't before due to his false imprisonment. He could be on a journey of self - discovery, trying to find his place in a world that has changed so much.
Dumbledore could also play a role even if Harry has left Earth. Maybe his spirit or some form of his magic reaches out to Harry from afar, guiding him on his journey and providing him with cryptic advice to face the challenges in outer - space - related magic.
Maybe the OC is a wizard from a different magical culture. For example, he could be from a far - flung wizarding community that was not directly involved in the war but has unique magical abilities. Neville could also be an important character, perhaps collaborating with Harry and the OC on projects to revive the magical plants that were damaged during the war.
Hermione could be one. She might use her vast knowledge of magic to help Harry figure out how to hatch the egg. Another could be Hagrid. He has a lot of experience with magical creatures, so he could offer advice on taking care of the egg and the soon - to - be - hatched creature.
Hermione and Ron would also be important characters. Hermione might be initially skeptical of Harry's newfound obsession with the Marauders. Ron, on the other hand, might be more easily swayed and join Harry in his attempts to be more like the Marauders.
A vampire hunter could be a key character. They might initially see Harry as a target too because of his association with the vampire. This would create a lot of tension as Harry and his mate have to either convince the hunter that they are not a threat or fight against them. And don't forget about Dumbledore (assuming this is in the Harry Potter universe). His reaction to Harry's new situation would be very interesting to explore.