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.
In this fanfiction, the main villain could be an ancient and powerful magical family who has been controlling the magical economy for centuries. They see Harry as a threat to their power and wealth. So they set up a series of elaborate traps and schemes. Harry, being inexperienced in economic matters, falls into their traps one by one, and as a result, Magical Britain starts to go bankrupt.
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.
Maybe in the fanfiction, Voldemort's return in a different way causes the wizarding government to spend all its funds on defense. They might have to buy expensive magical weapons, hire an army of aurors, and build fortified defenses. This over - expenditure could lead to bankruptcy not just of the wizarding part of Britain but also have a domino effect on the non - magical part as the two economies are likely connected in some ways. Also, the fear of Voldemort could stop all trade and tourism, further worsening the situation.
The goblins themselves could be the main antagonists. They are in charge of Gringotts and if they are greedy and corrupt, they would oppose any attempts by Harry to expose their wrongdoings that could lead to the bank's bankruptcy. They might try to stop Harry by using their magical skills and the defenses of the bank.
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.
Well, perhaps Harry discovers some major financial mismanagement in Gringotts. Maybe he finds out that the goblins have been embezzling funds or making really bad investments. This could lead to a situation where the bank is on the verge of collapse and Harry, being the hero he is, decides to expose the truth and in the process, bankrupts the bank as all the secrets come to light.
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.
It could be a new character created by the fanfiction author. Maybe a powerful wizard who was once shunned by the wizarding community and now wants revenge by stealing magic.
A dark wizard who has merged the dark arts with Wonderland's magic could be the main villain. He might have created some sort of dark Wonderland where all the creatures are under his control, and Harry has to break this control to restore balance.