It could be the wizarding authorities. If they discover that Vernon has been abusing Harry Potter all these years, they might decide to arrest him for child abuse. Even though they are in the wizarding world and Vernon is a Muggle, they could still have some jurisdiction over the well - being of a young wizard like Harry.
Maybe one of his co - workers at the drill company. If there's a power struggle or some sort of internal feud, a co - worker could tip off the authorities about Vernon's unethical business practices. For example, if Vernon has been taking credit for other people's work or stealing company funds to support his family's lavish lifestyle, a disgruntled co - worker might be the one to expose him and lead to his arrest.
It could be Harry Potter himself. He has been a victim of her tyranny and might finally find a way to expose her once and for all.
The Ministry of Magic could be responsible. They might be jealous of Dumbledore's power and popularity. They could see him as a threat to their own authority and come up with some false charges to arrest him. For example, they could claim he was hiding information about a dangerous dark wizard.
Maybe a mysterious new character in the fanfiction. This character could be from Adrien's family's past, someone with a vendetta against his family, and decides to start by getting Adrien arrested to disrupt the family. For example, if Adrien's family wronged this character's family long ago, they see Adrien as a target to take revenge on the whole family.
It could be an overzealous security guard. If Rachel was at a high - profile event and the security guard misinterpreted her actions as something threatening or against the rules, he could be the one to call the cops and get her arrested.
It could be Danzo. He has always been a bit of a shadowy figure with his own motives in the Naruto series. He might see Naruto as a threat to his power and influence within the village and engineer a situation where Naruto is executed.
It could be the students. They might think Snape is too gloomy and old - fashioned in his appearance. So, as a bit of mischief or maybe out of kindness, they use their magic skills to give him a makeover. For example, Harry Potter and his friends could be behind it, using spells they learned in their Defense Against the Dark Arts class.
It could be Voldemort. He might have used his influence over some Death Eaters within the Ministry of Magic to frame Dumbledore. By getting Dumbledore out of the way, Voldemort could have a free hand to carry out his evil plans in the wizarding world.
Perhaps Vernon is caught up in a wizarding - related incident without realizing it. He might accidentally help some dark wizards thinking they are just normal business partners. When the wizarding world realizes his unwitting involvement, they arrest him to question him about the dark wizards' plans. It could also be that his mistreatment of Harry finally catches up with him in a legal way. For example, if there are laws in the wizarding world about the proper treatment of magical children in non - magical households.
Another theme is family. Since they are related, albeit reluctantly in the original story, fanfictions often explore what it means to be family. They might show how Harry and Vernon could form a strange but real family bond.
One great fem Harry Potter and Vernon Dursley fanfiction is 'A Different Perspective'. It explores how a female Harry Potter might interact with Vernon in a more complex way than in the original series. The author really delves into the characters' personalities and how they would clash or, surprisingly, sometimes find common ground. It's an interesting read that gives a fresh take on the relationship between these two characters.