There could be other female characters like Valerie. As a ghost hunter, she might be intrigued by Danny's new charm and it could lead to some intense and exciting interactions between them in the fanfiction.
Sam is also important. She's Danny's friend and in some fanfictions, she might react in different ways to Danny's new 'Ladies Man' status. Maybe she's jealous or tries to help him manage this new side of himself.
There might be a fanfiction where Danny, as a 'Ladies Man', gets into some comical situations with different female characters from the show. For example, he tries to impress Paulina but keeps getting interrupted by his ghost - fighting obligations, which makes for a really fun read.
Obviously, the main character would be Danny Phantom himself, but in two different forms or versions. One would be the original Danny Phantom from the canon source, and the other would be a version created by the fanfiction. There might also be his friends like Sam and Tucker who could play important roles in helping the two Dannys understand each other and deal with any issues that arise from their meeting.
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.
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.
His friends like Sam and Tucker are likely to be main characters too. They usually support Danny in his adventures and add a human element to the story. Sam with her gothic style and strong will, and Tucker with his tech - savvy skills are important parts of Danny's world.
In many fanfictions, there could be new characters created specifically for the Renegades. These might be other half - ghosts or humans with special abilities that complement Danny's. For example, a character who can manipulate time in a small way to help the group in battles.
Jazz, Danny's sister, often plays an important role. She might use her psychological knowledge and her understanding of Danny to try to solve the mystery of his disappearance. And of course, some of Danny's ghostly foes might also be involved, as their actions could be related to his vanishing.
Well, clearly Danny Phantom is likely to be one of the main characters. And since it's about devils, there must be some devil characters as well. Maybe there's a lead devil character that Danny has to face off against.
Well, obviously the twins would be main characters. They could be named something like Jake and Jill. Danny himself would also be a main character as he would likely be involved in their story, either as a mentor or a friend. Then there could be other recurring characters from the original Danny Phantom series like Sam and Tucker, who might help the twins adjust to their new situation.
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.