Perhaps in the fanfiction, Danny discovers that there is a threat in the past that could change the future in a very bad way. He, along with Sam and Dani, time - travels to stop it. Along the way, they meet younger versions of their friends and family. Dani starts to understand more about her family's history and her own place in it. Sam has to deal with the differences in the past's social norms compared to their time. And Danny battles villains from the past who are trying to take over the future using the knowledge of time travel they accidentally introduced.
The plot could involve Dani finding a time - travel journal written by an ancestor. She shows it to Danny and Sam, and they decide to follow the clues in the journal. They travel to different times, each time facing a new challenge related to the power of time. In one time period, they have to save a village from a natural disaster that was actually caused by a time - traveling villain. Sam uses her scientific skills to try and fix the time - related problems. Danny and Dani use their ghost - related powers to fight off any threats, and throughout the journey, they learn more about the true nature of time and how it affects their family.
The plot could center around the emotional journey. Sam may experience a range of emotions from joy to fear. Danny could be there to comfort and encourage. They might also face difficulties such as financial concerns. For example, they'll need to think about buying baby stuff, finding a bigger place if needed. And as the pregnancy progresses, they'll have to start thinking about Dani's future, like education and what kind of life they want to provide for the child.
In the time travel fanfiction, their relationships could become stronger. Traveling through time together means they rely on each other more. Danny, as the more experienced one in dealing with the supernatural, would protect Sam and Dani. Sam, with her intelligence, would be the one to figure out time - travel puzzles, making Danny and Dani admire her more. Dani, being their daughter, would grow closer to her parents as she sees them in different historical situations and they work together to overcome difficulties.
Maybe Dani is not really Danny's clone in the way they thought. There could be some other mysterious force or entity that had a hand in her creation, and as they dig deeper into her origin, they find out that she has a much greater destiny than just being Danny's 'daughter' in a sense. This would completely change the dynamic of their relationship and the direction of the story.
One possible plot could be that their daughter inherits Danny's ghost powers. She might struggle to control them at first, just like Danny did. Sam and Danny would be there to guide her, teaching her about the importance of using her powers for good. There could be a new villain in town who targets their daughter because of her unique half - ghost nature. And she has to learn to use her powers and the knowledge passed down from her parents to defeat the villain.
One possible plot could be that there's a school talent show. Danny and Dani both decide to enter, but they want to keep their singing abilities a secret from the other because they're not sure how the other will react. As they practice in secret, they start to discover new things about themselves and their powers through the music.
Another possibility is a time - travel fanfiction. Danny and Dani accidentally travel back in time and have to figure out how to get back. Along the way, they meet younger versions of their friends and family and have to make sure they don't change the future too much. This could explore their relationship in a different setting and also show how Dani's powers might be different in the past.
One possible story could be that Dani travels back in time to prevent a major disaster in the Danny Phantom world. Maybe she goes back to the time when the portal was first opened and tries to stop it, which would change the entire course of events in the series.
She could travel to different alternate timelines. For example, a timeline where Danny never became a half - ghost. Dani's presence in such a timeline could cause all sorts of chaos as she tries to figure out how to get back to her own timeline while also dealing with the differences in this new world.
One idea could be that Danny and Sam travel back to the founding of Amity Park and accidentally change something small that has huge consequences in the present. For example, they might stop the first settler from building in a certain spot, which then changes the layout of the whole town and where ghosts can enter from in modern times.
One idea could be that Danny and Sam accidentally travel back to the age of dinosaurs. They have to figure out how to survive among the giant creatures while also trying to find a way back home. Maybe they discover a time - traveling dinosaur that helps them in some way.