In this kind of fanfic, perhaps Harry has finally had enough of the Dursleys' mistreatment. He might use his magic in a moment of rage. Maybe he starts by levitating Dudley to teach him a lesson after one too many taunts. Or he could use a spell to make Aunt Petunia's precious china smash, as a way of getting back at her for all the years of neglect and cruelty.
The main characters are Harry, who has reached his breaking point with the Dursleys. His pent - up anger and frustration towards them finally explodes into action. The Dursleys, on the other hand, are the recipients of Harry's wrath. Uncle Vernon, with his blustering and bullying ways, Aunt Petunia, who has always been cold and distant, and Dudley, the spoiled brat. There could also be appearances from characters like Dumbledore, who might show up to either reprimand Harry or offer some kind of guidance depending on the nature of the attacks.
It could be that a non - human magical being, like a centaur or a house - elf with a strong sense of justice, takes Harry from the Dursleys. They might see the abuse and neglect he endures and decide to act. This could lead to Harry having a completely different perspective on the magical world as he's exposed to aspects of it that are not typically part of a human - centric view.
In this fanfic, the Potters could have faked their deaths all along. They come back to rescue Harry when they find out how horribly the Dursleys are treating him. They might bring some magical creatures with them to help. For example, a phoenix that can heal Harry if he has any injuries from the Dursleys. Then they take Harry with them on a magical journey to a hidden wizarding community where they can all be safe and happy.
The plot twist could be related to Snape's true motives. He might be under an Unbreakable Vow to rescue Harry from the Dursleys. In the process, Harry realizes that Snape is not as bad as he seems. This could lead to a complete change in their relationship. Harry could start to trust Snape, and Snape, in turn, could teach Harry some unique magic that he has never learned before, which is crucial for the upcoming battle against Voldemort.
Perhaps in this fanfic, Severus doesn't just save Harry physically from the Dursleys. He also saves Harry from the emotional and psychological damage that the Dursleys have been inflicting on him. Severus, having his own traumatic past, might be able to relate to Harry on a deeper level and starts to mentor him in ways that Dumbledore never could. This could lead to a completely different Harry, more confident and less impulsive.
Well, one possibility could be that the Dursleys suddenly realize Harry's importance and the power he holds. They might see how he could bring them some sort of status or protection in the wizarding world. So, they start to accept him, change their attitude towards him, and perhaps even help him in his magical studies in secret.
In some interpretations, it could be that Harry finally snaps after years of abuse from the Dursleys. Maybe they pushed him too far one day and in a fit of rage, he uses his magic to end their lives. It's a very dark and extreme take on the Harry Potter universe.
Maybe Harry uses magic to make their house a mess. He could turn Dudley's room into a pigsty or make Aunt Petunia's precious china float and then smash. It's his way of getting back at all the years of mistreatment.
Perhaps Harry sues the Dursleys for false imprisonment. He realizes that all those years of being confined to his room or the cupboard were illegal. He enlists the help of Hermione, who is well - read in both wizarding and Muggle laws. They present a strong case against the Dursleys. As a result, the Dursleys face public humiliation in their neighborhood, and Harry finally gets the justice he deserves, while also starting to heal from the trauma of his childhood.
It could start with a build - up of small incidents. For example, the Dursleys constantly belittling him even after he has proven himself in the wizarding world. Then, one major event, like the Dursleys trying to sell his magic items or preventing him from going back to Hogwarts, causes Harry to snap. His killing of the Dursleys could then lead to a search for redemption or a fight against those who want to punish him unjustly, as he was pushed to his limits by their cruelty.