Another possibility is that they are simply on a retreat. After all the chaos and danger in the UK, they choose Australia as a place to relax and regroup. They could discover new forms of magic that are specific to Australia, like Aboriginal magic. This could open up new perspectives for them in their magical studies and adventures.
In some fanfictions, they might go there to search for something. Maybe they are looking for a magical artifact hidden in Australia. It could be a powerful charm or a lost spellbook that could help them in their fight against the Dark forces.
Perhaps they discover a long - lost vault. It could be a vault that contains powerful artifacts or important secrets about the wizarding world. This discovery would likely put them in danger as various dark forces would be interested in getting their hands on whatever is in the vault.
Perhaps they get involved in the American wizarding politics. The political situation in the American wizarding world might be different from that in the UK. Harry and Hermione, with their experience from the fight against Voldemort, could contribute to solving some problems in the American wizarding community, like issues related to the secrecy of magic in a more urbanized and diverse American society.
It might be related to Hermione's research. She may have read about some unique magical phenomenon in Australia that she wants to study first - hand. And Harry, being her loyal friend, goes along with her. For example, there could be a special type of plant with healing properties that only grows in certain parts of Australia.
Well, they might change some important events. For example, they could prevent certain tragedies from happening in the wizarding world. Maybe they'd save some characters who died in the original timeline.
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.
In fanfiction, they might relive their old memories. They could visit their favorite spots like the library where Hermione used to study all the time. Maybe they would share their experiences after leaving Hogwarts with the new students.
Well, they could change their own relationships. Perhaps Hermione would be able to help her younger self be more confident. Ron might stop himself from making some of the silly mistakes he made in the past. And Harry could get to know his parents better. They could also influence the development of magic in Hogwarts. For instance, introduce some new spells or magical concepts they learned in their original time.
In fanfiction, they might initially face hostility from some at the Burrow. Since Harry and Draco have a history of enmity, the Weasleys might be suspicious of Draco. However, as the story progresses, they could gradually come to understand each other. For example, Draco might show a different side of himself, like his knowledge of certain magic that could be useful to the Weasleys. And Harry could act as a mediator between Draco and the others at the Burrow.
In such a fanfiction, they might face new magical creatures unique to Australia. For example, the Drop - bear, which could be a fun and dangerous encounter for the Potter family. They may also have to adapt to a different magical community with its own set of rules and traditions.
There's a possibility that he'll face new challenges. It could be a place full of dark magic or dangerous creatures. Harry would have to use his wits and skills to overcome these challenges, and this could be a great opportunity for him to grow as a wizard.