Well, it could be about power dynamics within the family. Vernon might be shown as having power over Petunia and misusing it in the fanfiction. It might also touch on themes of neglect or emotional abuse, which are sadly common in real - life family situations and can be explored in this fictional context.
It's hard to say it's a widely popular genre. While there are fans who enjoy exploring the more disturbing aspects of fictional relationships, such as abuse in this case, it's likely a smaller subset of the fanfiction world. There are probably only a few groups or individuals who are specifically interested in this type of Vernon - Petunia dynamic. It may not be as popular as more positive or romantic fanfiction themes, but it still has the potential to attract a dedicated readership within its own niche.
One possible reason for Petunia never marrying Vernon in fanfiction could be to explore an alternate universe where the Dursley family dynamic is completely different. Maybe the author wants to focus on Petunia's own personal growth and independence outside of a traditional marriage. It could also be a way to introduce new and interesting plotlines, such as Petunia pursuing a career or having different relationships with the wizarding world.
Yes, there are some out there. You can start by looking on fanfiction platforms like FanFiction.net or Archive of Our Own. Some writers might explore an alternate universe where Vernon and Petunia show love towards Harry in a more positive way, perhaps due to a change in circumstances or a different understanding of his situation.
One possible plot could be that Harry shows a special talent early on that Vernon and Petunia recognize as something extraordinary. This makes them see Harry not as a burden but as a valuable part of the family. They then start to love and protect him, and this changes Harry's life completely. He no longer has to endure the abuse and neglect he faced in the original story.
One common theme is redemption. Often, Vernon is depicted as having a chance to redeem himself for his past bad treatment of Harry. Another theme is the discovery of common ground. For example, they might find out they both have a love for a certain type of food or a shared fear. And family is also a theme. Despite their differences, they are still family in a way, and fanfictions sometimes explore how that family bond can be mended or redefined.
Another theme is the contrast between the Muggle and magical worlds. Since Petunia is a Muggle and Snape is a wizard, their interactions can highlight the differences and difficulties in bridging those two worlds. For example, in some fanfictions, Petunia's envy of Snape's magical abilities is a central part of the story. It shows how the divide between the two worlds can create complex emotions.
One common theme is redemption. Often, Petunia is portrayed as having a chance to redeem herself for her past treatment of Harry. For example, she might finally show some love or understanding towards him.
There could also be themes related to social abuse. Sasuke might isolate Naruto from their friends or the village in the fanfiction. By doing so, he makes Naruto feel alone and unwanted, which is a form of abuse that can have a deep impact on Naruto's character development in the fictional story.
One common theme could be the exploration of Sasuke's emotional turmoil. Since Itachi is abusing him in this fanfiction, Sasuke might be shown as confused, angry, and deeply hurt. Another theme could be the power dynamic between them. Itachi being the abuser might have a significant amount of power over Sasuke, which could lead to themes of helplessness on Sasuke's part. Also, themes of revenge might be present. Sasuke might be constantly thinking about getting back at Itachi for the abuse, which could drive the plot forward in the fanfiction.
She might become more self - reliant. Without Vernon, Petunia could focus on her own needs and wants. She could explore her own interests, like gardening or painting, which she may not have had the chance to do in a marriage. This would give her a chance to develop her own identity, separate from the role of a wife.