I'm not sure specifically as there could be many different takes in fanfiction. But generally, it might involve Danny Phantom having some sort of difficult or 'bitter' encounter with a character he has a past with, perhaps a ghost he thought he'd never see again or a former enemy turned acquaintance in a strange new situation.
Well, Danny Phantom would surely be one of the main characters. And probably the character or characters he has this bitter reunion with. It could be a powerful ghost like Vlad Plasmius or maybe an old friend who has turned against him.
In this fanfiction, it could be that Danny Phantom meets a Danny Phantom from a parallel fan - made story. At first, they don't trust each other. But as they learn more about each other's worlds, they realize that there are some common elements that are being threatened. It could be that a powerful ghost is trying to rewrite all the fanfic universes related to Danny Phantom. So, they must combine their strengths and knowledge to stop this from happening.
The plot could be centered around a mystery. A strange series of events start happening in Amity Park and it seems to be related to some new technology that Dr. Drakken has created. Danny Phantom investigates and runs into Shego. They start off as adversaries but as they dig deeper, they realize they need to work together to solve the mystery. Maybe there's a hidden force that is using Drakken's tech to open portals to the Ghost Zone and release dangerous ghosts, and only Danny and Shego can stop it.
Well, in the 'danny phantom is a lion fanfiction', it could be that Danny is cursed to become a lion at times. As a lion, he discovers new aspects of the ghost world. For example, there could be a group of lion - like ghosts that only communicate with him when he's in lion form, and they tell him secrets about his powers or his family's past that he didn't know before.
One possible plot could be that Izuku discovers the existence of Danny Phantom through some kind of interdimensional event. He then tries to learn from Danny's way of handling his powers and his secret identity, applying those lessons to his own journey as a hero in training.
A possible plot could be that Maddie is trying to create a device that can communicate with ghosts in a more peaceful way. Danny, being half - ghost, is both excited and a bit worried about this. Lemon, who has a more open - minded view on the supernatural, encourages Maddie. Danny then gets involved in the project, and they face many challenges along the way. For example, some other ghosts might not want humans to be able to communicate with them so easily, and they try to stop the project. This could lead to a story full of drama, with Danny having to use his powers to protect Maddie and Lemon while also trying to support Maddie's scientific goals.
One idea could be that Danny discovers a new ghostly power that he uses to take revenge on a group of bullies who have been tormenting his friends. He could use his intangibility in a creative way, like sneaking into their lockers and making their things disappear.
The plot could involve some sort of mystery related to the pregnancy. Like, there could be a ghostly force that is either helping or hindering the pregnancy. And they have to figure out what it is and how to deal with it. Also, their friends like Tucker could play important roles in supporting them.
One idea could be Danny Fenton having to deal with a new ghostly enemy that can manipulate time, making his double life as Danny Phantom even more chaotic. Another could be Danny trying to balance his high school life, including exams and relationships, while also facing a ghost invasion that only he as Danny Phantom can stop. Or perhaps a story where Danny Phantom discovers a hidden power within himself that has a connection to his human side, Danny Fenton.
The plot could change in terms of her love interests. Instead of the typical male - led romantic arcs, there could be new female - centered ones. For example, she might have a different type of relationship with a male character, where she takes the lead more often.