Another interesting angle is to write about how they deal with external family pressures. Suppose one family member is constantly interfering in their relationship. The couple has to work together to set boundaries while still maintaining family harmony. This can lead to a lot of character growth and development in the fanfiction.
One idea could be exploring the backstories of the minor characters in Happy Valley in more depth. For example, the life of a local shopkeeper and how they interact with the main characters during the events of the show.
One idea could be to explore the backstory of the killer more in - depth. Maybe he had a tragic past that led him to this cycle of killing. Another idea is to create an alternate ending where the main character doesn't keep reliving the day but instead finds a way to break the cycle completely before the final confrontation. Also, a fanfiction could focus on a different character from the movie experiencing the time - loop instead of the main protagonist.
One idea could be a human character who befriends Mumble and helps him spread his message of dancing in the human world. Maybe the human is a scientist studying penguins and is inspired by Mumble's unique behavior.
You could also write a fanfiction where an OC is a detective investigating some of the club's activities. Happy is assigned to keep an eye on the OC, and over time, they develop an unexpected bond. This would involve a lot of tension and mystery, as the OC tries to uncover the truth while Happy tries to protect the club's secrets.
One idea could be a story where the phantom marriage is a result of a magical curse. The characters have to figure out how to break the curse while dealing with the strange relationship dynamic. Another could be a modern - day take on phantom marriage where it's a virtual or long - distance relationship that has some elements of mystery.
In some naruto marriage contract fanfiction, there might be a plot where Naruto is forced into a marriage contract due to political reasons. This could lead to all sorts of drama and character development. He might have to deal with his own feelings towards the person he's contracted to marry, while also trying to balance his duties to the village. It could also explore how the other characters react to this unexpected situation.
One interesting idea could be the complex relationship dynamics that develop due to the marriage contract. For example, Harry might have to navigate new social expectations and deal with characters who have different motives regarding the contract. It could also lead to unexpected alliances or rivalries within the wizarding world.
A plot could involve a character who is forced into a marriage due to some archaic part of the marriage law. The story could be about their struggle to break free and change the law for others in the same situation. They might meet an attorney who is also an advocate for marriage law reform and together they start a campaign. This would involve researching different cases, gathering evidence of the law's negative impacts, and presenting it to lawmakers. There could be a lot of drama as the character's family and the establishment try to stop them from making changes.
For a 'a marriage of true minds fanfiction', you might consider setting it in a different time period or location. This would add a new layer of complexity to their relationship. For example, if they were in a historical setting, they would have to deal with the social norms and expectations of that era, which could either strengthen or strain their marriage of true minds.
One interesting idea could be the exploration of how the characters' personalities clash or blend in an arranged marriage setting. For example, Bella's independent nature might be at odds with the traditional expectations of an arranged marriage in the Twilight universe.