One possible fanfic could be about Petunia Dursley finding a magical toy that once belonged to Harry Potter's parents. Maybe she discovers it in the attic and it starts to show her memories of Lily and James Potter. She realizes that she has been wrong about Harry all along and decides to change her attitude towards him.
By focusing on their shared past traumas. For example, both have had experiences related to Lily's death in different ways. Harry lost his mother, and Petunia lost her sister. They could start to bond over this common pain and gradually move towards a more positive relationship.
A common theme is also the exploration of the Muggle - wizard relationship. Dudley, being a Muggle, and Harry, a wizard, their interactions can show how the two worlds can co - exist and understand each other better. Some fanfics also touch on the idea of Dudley feeling left out or inferior because of his lack of magic, and how he overcomes these feelings to build a better relationship with Harry and the wizarding world.
One common theme is redemption. Many fanfics focus on Dudley realizing his past mistakes and trying to become a better person. Another theme is the exploration of his relationship with Harry. Since they had a rocky start, fanfics often explore how they can reconcile or at least understand each other better.
They are often portrayed as the villains. Their years of treating Harry badly are brought to light. They might look scared and out of place in the wizarding courtroom, with all its strange sights and magic.
In many 'Harry Potter x Vernon Dursley fanfic', the theme of growth is prevalent. Both characters can grow and learn from each other. For example, Harry might teach Vernon about the importance of acceptance, while Vernon could show Harry some aspects of the Muggle world he hadn't considered. Also, the theme of power struggle can be seen. Vernon has a certain kind of power over Harry in the Dursley household, and fanfics might explore how that power shifts as Harry grows older and more powerful in the wizarding world. And of course, there's the theme of forgiveness. Given how horribly Vernon has treated Harry in the books, some fanfics will focus on whether Harry can forgive him or not.
In a more comical plot, the lemon could be a mischievous magical object that keeps causing chaos in Petunia's house. It might make things float or turn into strange creatures. Petunia, being the uptight person she is, has to deal with this lemon - induced mayhem while also trying to keep up appearances in front of the neighbors. This could lead to some really funny situations and a change in her attitude towards the strange and magical over time.
A fanfic could connect them by having a toy that was passed down from Lily Potter to Harry, but Petunia has kept it hidden all these years. When Harry discovers it, it causes a big conflict as Petunia doesn't want to let go of the last piece of her sister she has in that way. But eventually, it could lead to a moment of reconciliation between them.
In many 'Harry Potter Dursley fanfiction' stories, the Dursleys are used as a contrast to the wizarding world. Their normal, mundane lives are juxtaposed with the magic and wonder of Harry's world. This can create interesting storylines where they are either forced to accept the magic or try to fight against it in their own stubborn ways.