Since I don't know the exact 'the ghost waltz story', I can't say for sure who the main characters are. But it could be a ghost as one of the main characters, and perhaps a dancer or a musician.
Without having read the 'the ghost waltz story', it's hard to determine the main characters. However, if it follows the typical pattern of such stories, there might be a human protagonist who stumbles upon the ghost waltz. And of course, the ghost or ghosts associated with the waltz would likely be main characters as well. There could also be a side character like a mentor or a friend who helps the protagonist understand the mystery of the ghost waltz.
Maybe there's a young girl who dreams of dancing the Christmas waltz and her mentor who teaches her. There could also be a group of friends who make the Christmas waltz a memorable part of their holiday together.
Perhaps an older gentleman and a young debutante. The older gentleman could be a bit of a relic from a bygone era, with strict ideas about how the waltz should be danced, and the young debutante is trying to break free from those traditional norms while still being polite.
It could be the waltz itself as a main element. Maybe it has a unique and spooky melody.
I'm not sure as I haven't read the novel specifically. But usually, in a novel like this, there would be a protagonist who is likely to be the one most affected by the 'darkness' and who has to waltz through it. There might also be a love interest or a mentor figure to help or complicate the protagonist's journey.
The 'the ghost waltz story' could be about a lot of things. It might tell the tale of a waltz that was created by a ghost, or a waltz that has the power to summon ghosts. Perhaps it's a story about a couple who were separated by death and their love is expressed through a ghostly waltz. Another possibility is that it's about a cursed waltz that brings misfortune to those who dance it, and this misfortune is somehow related to the presence of ghosts. There could also be a historical aspect to it, like a waltz that was danced during a time of great tragedy and now the ghosts of those who perished during that time are associated with the waltz.
I'm not sure specifically as I don't have detailed information about this visual novel. But it's likely to have the princess as a main character. There may also be a prince or other noble characters.
Since I don't know the story in detail, I can't say for sure who the main character is. But from the title, it seems that the 'fat man' is likely to be the main character.
I'm not entirely sure as I haven't read the specific 'waltz into darkness novel' in detail. But usually, the protagonist is an important character. He or she is likely to drive the story forward, facing various challenges and making crucial decisions throughout the novel.
In 'the ghost story', the main characters could be the people who encounter the ghost. Maybe a group of curious kids or a brave investigator.
As I don't know the particular '1930 ghost story', it could have a protagonist like a young journalist who is investigating the strange happenings. There might also be an old caretaker of the haunted place who has some secrets.