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.
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.
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.
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.
Gray and Juvia's offspring could also be central characters. They could have an interesting mix of ice - make magic and water magic. Maybe they struggle with controlling their powers at first, just like their parents did, but in different ways. And their relationships with the other next - generation characters could be complex, adding depth to the story.
The children of Natsu and Lucy would be great main characters. They could inherit their parents' powers and personalities. For instance, having the same determination as Natsu and the intelligence of Lucy.