Obviously, Danny Phantom would be the main character. He would be the one bringing his unique set of powers to the Civil War setting. There might also be some key historical figures from the Civil War like Abraham Lincoln. Maybe Danny has an encounter with him and helps him in some way.
In the 'Danny Phantom in the Civil War' fanfic, perhaps Danny is somehow transported to the time of the Civil War. He could find himself in a moral dilemma. On one hand, he wants to stop the bloodshed, but on the other, he doesn't want to interfere too much with history. He might end up using his powers in a more subtle way, like using his ecto - energy to heal the wounded without being noticed.
Obviously, Danny Phantom and Ember would be the main characters. Danny is the half - ghost protagonist who is being raised by Ember. Ember, a ghost with music - related powers, would play the role of his caretaker or mentor in this fanfiction.
Obviously, Danny Phantom is one of the main characters as the title implies he's the one doing the pranking. And then, members of the Justice League like Superman, Batman, Wonder Woman, Flash, etc. would be the ones being pranked.
In a crossover, characters from the other franchise might betray Danny. For example, if it's a crossover with a show about vampires, a vampire character who seems friendly at first could betray Danny for his ghost powers. They might want to use his powers for their own dark purposes. Another likely candidate could be a character who is jealous of Danny's abilities. Maybe in a crossover with a superhero world, a sidekick who feels overshadowed by Danny's powers and popularity might be the one to betray him.
Well, apart from Danny, Sam and Tucker, there could be other characters from the Danny Phantom universe. For example, Valerie Gray, who has her own vendetta against ghosts. When Danny reveals his identity, she might have a really interesting reaction. She could either see him as a threat or realize that he's not as bad as she thought. And then there are the teachers at school. They might notice some changes in Danny after his identity is revealed and start to suspect something strange is going on.
In addition to the ghosts, there might be some human characters that are important in the 'phantom city danny phantom fanfiction'. They could be Danny's friends or family members who get involved in the events of the Phantom City. Their reactions to the supernatural world and their interactions with Danny and the ghosts would add an interesting dynamic to the story.
A padawan who has just come of age and is now thrust into the chaos of the civil war could be a main character. Their inexperience and fresh perspective could add an interesting dynamic.
Obviously, Danny Phantom and Dan Phantom are the main characters. Danny is the original form, a heroic character, and Dan is his more evil and powerful transformation.
Sometimes, there are original characters in these fanfictions. For example, a merman elder who guides Danny in the underwater world. This character can introduce Danny to the rules and culture of the merman society. Another could be an underwater villain who wants to use Danny's powers for their own evil purposes, adding conflict to the story.
In many Danny Phantom sword fanfictions, Danny is front and center. He's the one who discovers the sword, whether it's in the Ghost Zone or some hidden place in Amity Park. Jazz, his sister, could also play a role. She might be skeptical at first but then get involved when she realizes the sword's significance. And there could be an antagonist, perhaps a powerful ghost who wants the sword for its own evil purposes.