Obviously, Captain Hook's daughter would be a main character. And Captain Hook himself would play a significant role as well.
Peter Pan could be another main character. His interactions with the daughter, either as an enemy or an unexpected ally, would be interesting. Also, Smee, Captain Hook's loyal crewmate, might be in the story a lot. He could act as a sort of mentor or protector to the daughter at times. And there could be a new character, like a mermaid who befriends the daughter and helps her understand the secrets of Neverland.
It could be about the daughter's adventures in Neverland. Maybe she tries to change the way pirates are seen there.
The main characters would most probably include Captain Hook himself. He's the central figure around which the story would revolve. Peter Pan would also be there as his constant opponent. Additionally, his crew members on the Jolly Roger might be important characters too. They could add depth to the story, showing how they interact with Hook and support or sometimes question his decisions.
It could be a damsel in distress. Maybe a princess who was captured by Hook's crew and he falls in love with her.
In some Captain's Hart fanfic, there could be antagonists that oppose Captain Hart. These characters are crucial as they create conflict and drive the plot forward. They could be rival captains or evil entities from other galaxies.
She is often rebellious. Since her father is a villain, she might want to oppose his ways and create her own path.
A mysterious figure from the captain's past could be a key character. Maybe this person was involved in the events that led to the promise in the first place. They could reappear and try to either help or hinder the captain in keeping the promise. Also, a young crew member who looks up to the captain could be important. Their naivete and admiration could add an interesting dynamic as they try to understand the weight of the captain's promise.
Obviously, the daughter herself would be a main character. She could be a strong - willed, intelligent young woman. Antonio Dawson would also be a central figure, guiding and supporting his daughter.
Since I don't know the exact 'captain cloud fanfic', I can only guess. Captain Cloud would likely be one of the main characters. There might also be sidekicks or companions like a little cloud sprite that helps him or a wise old cloud hermit who gives him advice.
There could also be new characters created specifically for the fanfic. For example, a mysterious girl who has the power to communicate with animals and teams up with Captain Underpants and the boys to stop an evil scientist from mutating all the pets in the town. This new character can add a fresh dynamic to the typical Captain Underpants story.
One interesting plot could be the daughter's struggle to break free from her father's villainous shadow. Maybe she tries to make amends for his wrongdoings in Neverland.