Another plot could be that the Dursley family gets involved in a magical adventure that has nothing to do with Harry. For example, they accidentally stumble upon a magical artifact that transports them to a different magical realm where they have to learn magic quickly to survive and find their way back home.
Another plot could be a time - travel scenario. A character goes back in time and changes the way the Dursleys treated Harry. As a result, they become a more loving and accepting family. This alteration in their relationship could have a huge impact on the entire wizarding world as Harry grows up with a more positive influence.
One interesting plot idea could be Dudley traveling back in time to when his parents first got married. He could see how his family's attitudes towards magic and the Potters were formed. Another could be him traveling forward in time to see the impact of Harry Potter's actions on the wizarding world and how it indirectly affects the Muggle world he lives in. Maybe he travels to a time when a major wizard - Muggle conflict was about to start and he has to use his new - found knowledge of both worlds to prevent it.
A great plot could be centered around Dudley and Harry being forced to work together on a project in the Muggle world that has some unexpected magical implications. This could lead to them understanding each other better and forging a new kind of relationship. For example, they might be involved in an archaeological dig that uncovers a lost magical artifact, and they have to keep it safe from both Muggle and wizarding thieves.
One idea could be that the Dursleys' constant mistreatment and abuse over the years gradually chip away at Harry's sense of right and wrong, making him more susceptible to dark influences. Another might be that they introduce him to dark wizards or artifacts that start to sway his view of magic towards the darker side.
Obviously, Vernon Dursley could be a main character. We could explore his thoughts and feelings more deeply, especially if the fanfiction takes a different turn on his personality, like making him more sympathetic.
It could be Dudley. He could have a character arc where he realizes the error of his ways in bullying Harry and decides to embrace the magical world. Maybe he discovers he has a unique magical talent that was hidden all along.
A possible plot could be a time - travel scenario where Harry and Petunia are sent back in time. They have to rely on each other to survive in the past, and in the process, they learn more about their family history and each other. This shared adventure could lead to a deeper understanding and a different kind of relationship between them.
You could also write about Naruto's family during a time of peace. How they interact with the other families in the village, and how they pass on the values of the ninja way to the next generation. It could include family outings, training sessions that are more about bonding than combat, and the family's role in maintaining the positive atmosphere in the village.
One idea could be exploring the relationship between Batman and Robin in a more emotional depth. Maybe Robin is going through a tough time at school and Batman has to balance being a mentor and a crime - fighter. Another could be a time - travel plot where the Bat - family gets sent to different eras in Gotham's history and has to adapt and still fight crime.
One idea could be exploring the family dynamics when the Avengers have to take care of a young superhero in training. It would be fun to see how they each contribute to the kid's growth, like Tony Stark teaching about technology and Captain America instilling values.