One common scenario is that Harry leaves Britain and goes to live in another wizarding community. He might feel that he can start anew away from the pain and memories of Britain.
Well, it could signify a very different take on the Harry Potter universe. Maybe in this fanfiction, the author wants to explore the idea of Harry Potter causing the downfall of the magical society in Britain for various reasons, like a radical change in his character or some extreme circumstances.
There could be personal consequences for Harry as well. He might face opposition and even threats from those who want to protect the status quo in Magical Britain. His friends and family could also be affected, either by being targeted or by being caught in the middle of the conflict between Harry and the establishment. However, this could also make him more determined to fight for what he believes is right.
One possible reason could be the corrupt system in Magical Britain. In some fanfictions, the Ministry of Magic is shown as being full of bureaucrats who are more concerned with maintaining power and the status quo rather than doing what's right. For example, they might be slow to respond to real threats or they could be discriminatory towards certain groups, like Muggle - borns. Harry, having grown up in a non - magical world and having a sense of justice, would naturally despise such a system.
Obviously, Harry Potter is the main character as he is the King of Magical Britain in this fanfiction. His friends like Hermione Granger and Ron Weasley are also likely to be important characters. They would probably be his advisors or help him in his various endeavors.
There's 'Harry Potter: Beyond the British Isles'. Here, Harry's departure from Magical Britain is due to his search for a real home. He has always felt like an outsider there. As he leaves, he embarks on a journey full of self - discovery and adventure, meeting all sorts of unique magical creatures and characters in far - flung places.
Well, perhaps in this fanfiction, Harry Potter accidentally casts a spell that has a domino effect on the magical economy of Britain. For example, he might mess up a powerful charm related to the wizarding currency, leading to a rapid devaluation. Or maybe he uncovers some dark secret about the Ministry of Magic's financial management that causes a mass panic and economic collapse.
Well, in some 'harry potter king of magical britain fanfiction', there's a plotline where Harry has to deal with dark wizards who oppose his rule. He uses his unique skills and the loyalty of his friends to fight them off. Also, there could be a story where he uses his position to improve magical education, perhaps by bringing in new subjects that were previously ignored, like advanced defensive magic for all years at Hogwarts.
It could be a corrupt wizard within the Ministry of Magic's financial department. He might be embezzling funds and using dark magic to cover his tracks. When Harry starts to dig into the strange financial situations in Magical Britain, this wizard tries to stop him by all means, which eventually leads to the bankruptcy as the situation gets out of control.
One possible plot could be that Harry discovers a dark secret about the Ministry of Magic, like they are using dark magic themselves to control the wizarding population. So he decides to expose them and in the process, the chaos that ensues leads to the destruction of magical Britain as it was known.