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.
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.
The wizarding world's reaction would be complex. On one hand, Harry's friends like Hermione and Ron might be conflicted. They know the Dursleys were awful to Harry, but they also believe in the value of life. Wizards who have a strong sense of justice might understand Harry's actions, especially those who have also faced prejudice or abuse. But the more traditional and law - abiding members of the wizarding community would condemn Harry, and the Ministry would likely try to arrest him, leading to a possible conflict between those who support Harry and those who don't.
I haven't actually come across a 'Dursleys kills Harry Potter' fanfiction. It's a rather disturbing concept considering how the story of Harry Potter is centered around his survival against Voldemort. The Dursleys are just part of his Muggle upbringing with their own brand of meanness. If there were such a fanfiction, it would probably change the whole trajectory of the story. For example, the wizarding world would lose its Boy Who Lived, and it would be interesting to see how the characters like Dumbledore or Hermione would react to such a tragic event.
There are likely 'Harry Potter Kills Dursleys' fanfictions. Fanfic writers often like to explore extreme scenarios. In this case, it could be a way to show how far Harry could be pushed. It might also be a commentary on the Dursleys' horrible treatment of Harry. But this goes against the somewhat forgiving nature of Harry in the original books.
Well, it might be that Harry snaps due to his ongoing struggle with Voldemort. After constantly being in a state of fear and having to fight for his life and the lives of his friends, he reaches his limit. He could turn against some of his friends who he feels haven't been fully supportive or understanding. His snapping could lead to a power shift in the wizarding world, as he may start to use his magic in more aggressive and unorthodox ways to protect himself and what he believes in.
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.
Well, it could be about Harry finally losing his patience with all the constant threats and dark magic. Maybe he decides to take a more aggressive approach against Voldemort and his Death Eaters, instead of always waiting for them to make the first move.
Perhaps Harry uses his influence among his friends. Hermione could help him find some loophole in the Muggle - wizarding laws regarding property. Ron might provide some comical support, like trying to use some half - baked spell to make the Dursleys uncomfortable enough to leave. In the end, Harry evicts them and takes over the house, turning it into a place that's more welcoming for himself and his wizarding friends when they visit the Muggle world.
Perhaps in the 'harry gives birth at dursleys fanfiction', there's a new form of magic introduced. Harry could have been affected by a magical experiment that causes this strange phenomenon. The Dursleys, who have always mistreated Harry, now have to face the consequences of having such a unique and unheard - of event happening in their house. They might be in a state of panic and confusion as they try to figure out what to do.
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.