Maybe he studied hard in the field of healing magic after leaving school. He could have apprenticed under some great healers and then got an offer to work at Hogwarts.
In fanfiction, Harry as a healer could also be involved in dealing with the effects of dark magic on students who accidentally encounter it. He'd have to use his knowledge of counter - curses and healing spells. For example, if a student was hit by a minor hex, Harry would need to figure out the right spell to reverse it and then heal any after - effects. He may also be in charge of teaching some basic first - aid magic to older students so they can help in minor emergencies around the school.
Neville Longbottom could also be considered a natural healer. He has a great affinity for Herbology. His skills in growing and understanding plants could easily translate into using them for healing. He could be the one to discover new uses for common and rare magical plants alike, perhaps creating poultices or potions from them to heal various ailments that the regular wizarding medical field hasn't fully explored yet.
Healer Pomfrey is significant in Harry Potter fanfiction as she represents the medical care within Hogwarts. In fanfics, she can be a stabilizer during chaotic times. For instance, when Harry and his friends are injured during their adventures against the Dark Arts, Pomfrey is there to patch them up. Her presence gives a sense of safety within the Hogwarts walls, even in the face of great danger.
Perhaps Harry has a vision or a prophetic dream where he sees himself as a healer, saving lives. This drives him to study hard in his Healing classes at Hogwarts. He also starts to research ancient healing techniques on his own. He faces some challenges, like some people doubting his ability because of his past as 'the boy who lived', but he overcomes them and works towards his goal.
Harry is the central figure, of course. However, some fanfictions might introduce new characters. For example, a young Muggle - born witch or wizard who Harry takes under his wing to teach about magic and healing. There could also be a former Death Eater who has reformed and now wants to learn the ways of healing from Harry to atone for their past sins.
In the fanfiction world, Harry might be the heir to Hogwarts if there was some sort of magical pact made generations ago. For example, perhaps one of his ancestors had a special role in the creation or protection of Hogwarts, and this role was passed down through the family. It could also be that his unique magical abilities, like his ability to resist Voldemort's attacks from a young age, are signs of a deeper connection to Hogwarts itself. This connection could be what designates him as the heir in the fanfiction's plot.
In Harry Potter fanfiction, Healer Pomfrey is often portrayed as a key figure in Hogwarts' medical wing. She is known for her strict yet caring nature. Fanfiction authors may expand on her backstory, perhaps exploring her training as a healer or her relationships with other Hogwarts staff members. Some stories might show her handling more complex magical maladies than what was seen in the original books.
One great 'Harry is a Healer' fanfiction is 'Healing Hands'. In it, Harry uses his unique experiences to bring a fresh perspective to the healing arts in the wizarding world. He has to deal with patients who are both physically and mentally scarred from the war, which makes for a really interesting read.
He could start by volunteering in the Hogwarts infirmary. There, he'd learn a lot from Madam Pomfrey. For example, how to handle different magical maladies. This hands - on experience would be the first step in his journey to become a healer.