Well, he might encounter unique magical creatures native to Australia. Maybe he'd come across the bunyip, a fearsome water - dwelling creature. He could also explore the Australian wizarding community, which might have different traditions compared to the UK's. For example, their use of magic in relation to the unique Australian flora and fauna could be really interesting.
He might encounter unique Australian wildlife on his way to school, like seeing kangaroos hopping around. Maybe he'll also have friends who are of different ethnic backgrounds due to Australia's multicultural society.
Perhaps in this fanfiction, Percy goes to Australia to find a hidden artifact that is crucial for the safety of the demigod world. Along the way, he teams up with local demigods (if there are any in the fan - created story). He would have to adapt to the Australian culture and environment, which is very different from what he's used to in the US. He might also face some new types of monsters that are native to Australia.
Perhaps Harry will meet some reclusive or mysterious figures in the new school. They could be ancient wizards who have been in hiding for years, or strange creatures that are able to communicate with humans. These encounters would surely add more excitement and mystery to Harry's time at the different school. He may also come across some students who have a different view on the wizarding war and Voldemort, which would make for interesting conversations and potential conflicts.
One possible plot could be Harry struggling to adapt to the strict discipline of military school at first. He might have conflicts with the drill sergeants who are tough on him. But as time goes by, he discovers his own inner strength and leadership skills, and eventually earns the respect of his peers and instructors.
There may be a group of students who are outcasts or have special powers that are not fully understood. Harry might befriend them, and they could all be main characters in the sense that they are central to the story's plot. They could be working together to uncover secrets about the school, themselves, or the magical world in general.
Well, he might make new friends who have different magical abilities or come from different backgrounds. Maybe he'll learn new spells or magical theories not taught at Hogwarts.
Well, it could be about Death taking on a form that can attend Hogwarts with Harry. Maybe it's there to protect him in a more direct way than the usual magical means. It might interact with Harry's friends, causing some confusion and also some revelations about the nature of life and death in the wizarding world.
Maybe Harry could struggle with the language at first. He might make new friends who introduce him to French wizarding traditions. And he could have adventures in the unique French school setting.