There could be a character like Nova, a young girl who has the ability to phase through solid objects like a ghost but is human. She uses this power to help the new generation of ghost hunters.
Definitely Danny's kids if he has any in the fanfiction universe. They could inherit his powers and have to learn how to use them while dealing with their own personal issues. Also, Sam and Tucker's children could be main characters. They might not have ghost powers but could be very tech - savvy and help in other ways, like creating new gadgets to fight ghosts.
A new character could be a half - human, half - ghost like Danny, but from a different part of the world with unique cultural ghost powers. For example, a character from Asia who can use ancient ghost - binding spells passed down through generations in their family.
Maybe a new student who has some psychic abilities that attract the attention of the ghosts in the school. This student could either be a friend or a foe to Danny, depending on how the story unfolds.
An ancient spirit that has been trapped in the urban jungle for centuries. It has its own motives and goals, and at first seems like a foe but later might become an ally to Danny.
A cool plot might be that the next - gen Danny Phantom characters face a situation where their powers are being slowly drained. They then have to go on a quest to find the source of this draining and stop it before they become completely powerless. It could involve meeting old enemies of Danny's who have new tricks up their sleeves.
Perhaps the new generation discovers a hidden realm in the Ghost Zone that was sealed off long ago. Inside, they find ancient powers and secrets that could either save or destroy the human - ghost balance. They have to make tough decisions on how to handle these newfound elements.
Obviously, Danny Phantom himself. And Hades, his supposed father. There could also be Danny's friends like Sam and Tucker. Maybe some Greek mythological figures such as Cerberus, the three - headed dog that guards the underworld.
There could be the children of the original Young Justice members. For example, a son or daughter of Robin who has inherited his detective skills and acrobatic abilities. They would be eager to prove themselves in the hero world.
Potential characters could include powerful ghost lords that Danny has to deal with. These could be ancient and very powerful ghosts who see Danny as a threat or an opportunity. There might also be some half - ghost characters like Danny, but with different origins. They could be his allies or enemies. And let's not forget the minor ghosts that populate the Ghost Zone, they could add flavor to the story, either by helping Danny or causing trouble for him.
Well, for the Danny Phantom side, Sam and Tucker could be involved. Sam might be jealous at first when other girls start showing interest in Danny. Tucker could be the one giving Danny advice on how to handle the harem situation. From other shows, if it's a crossover with a magical girl anime, characters like Sailor Moon could be part of the harem. Her kind and powerful nature would make an interesting dynamic with Danny. Another could be Kim Possible. She's a strong and capable girl who would likely be intrigued by Danny's powers and get involved in his adventures, and potentially develop feelings for him.