Perhaps Harry will run into an old wizard who has been in the hospital for a long time. This wizard has a lot of stories about the old days of the wizarding world and gives Harry some valuable advice.
Maybe Harry is injured during a Quidditch match and has to be rushed to the hospital. There he might meet some interesting new characters, like a healer with a mysterious past.
Well, Harry could be really confused at first. Ouran is a very different world from Hogwarts. He might be shocked by the opulence of Ouran Academy and the strange club system there. Maybe he'd try to find a way to fit in while still being true to his wizard self.
Perhaps he'll meet an old patient who has been in the hospital for a long time. This patient could tell Harry some long - forgotten stories about Hogwarts in the past. There could also be a chance that he meets some other students who are also in the hospital for various reasons, and they might form a new friendship or alliance.
Maybe he'll encounter a group of young wizards and witches who are also patients. They could form a bond and share their magical experiences. For example, they might talk about their different encounters with magical creatures outside of Hogwarts. This group could also play a role in helping Harry solve a problem that arises during his time in the hospital, like a malfunctioning magical device that is causing chaos in one of the wards.
In the 'Harry goes to the hospital fanfic', it's possible that Harry is injured during a Quidditch match. He is then rushed to the hospital. There, he could discover a hidden part of the hospital that has some ancient magic stored. He might also have some deep conversations with his friends who come to visit him about their future plans and the current state of the wizarding world.
He might meet international aurors. These are highly skilled wizards from different countries who are experts in dark wizard catching. They could teach Harry some new combat spells.
He could meet Fleur Delacour's family. Since Fleur is from France, her family might be an important part of the French wizarding community that Harry interacts with.