Well, without more information about the 'Ghost Ship Girl Story', we can only speculate. The girl is the central figure, no doubt. But there could be antagonists too. It could be an evil spirit that haunts the ship and tries to prevent the girl from uncovering the truth. There might also be a helpful spirit, perhaps a former crew member who guides the girl through the maze - like corridors of the ship. And perhaps there's a character from the girl's own world, like a friend or a family member who she is trying to get back to, and this longing drives her actions on the ghost ship.
Obviously, the main character is the little girl. She is likely at the center of whatever events unfold on the ghost ship.
The main characters could include the lawyers representing different parties in the trial. There might also be witnesses who have some knowledge about the ghost ship, like sailors who saw it adrift or people who were involved in its discovery.
There could be a brave sailor who stumbles upon the ghost ship.
The main character is the little girl, as the title 'Ghost Ship A Little Girl's Story' clearly indicates.
There might be a young and brave sailor as one of the main characters. He could be the one who first discovers the strange things happening on the ship during the last voyage. Also, perhaps an old seaman who has some knowledge about the ship's past and might be able to give some clues about why it has become a 'ghost ship' now.
Maybe there's a young adventurer who stumbles upon the ghost ship. There could also be an old sea captain who has heard rumors about the ship all his life and finally decides to investigate. And perhaps there are some spectral characters that are part of the ship's crew, like a ghostly first mate who has some sort of connection to the ship's past and the mystery surrounding it.
Often, there will be the sailors who discover the ghost ship. They are the main characters as they are the ones who experience the events of the last voyage.
Since it's a Sigma Force short story about a ghost ship, the main characters would be from Sigma Force. There could be a character who is the brains behind the operation, someone highly intelligent and analytical. Another character could be the muscle, a physically strong individual who is not afraid to take on any threats on the ship. And perhaps there's a character who has some sort of sixth sense or intuition that helps them navigate through the mysteries of the ghost ship. They all work together as a team, each bringing their own unique abilities to the mission.
I don't know who the author of this work is. It could be an independent writer or someone not widely known yet.
Most likely, the main character is the ghost girl herself. She could be a lonely spirit with her own story to tell.