Perhaps there is a young detective - type character who is determined to solve the mystery of the monster house. There might also be a local hermit who knows some secrets about the house and helps or hinders the main character. And of course, there could be some sort of supernatural entity that is either the cause of the house being a monster or is trapped inside the house.
Since I don't know the specific 'monster a graphic novel', it's hard to say. But it could have the monster itself as a main character. There might also be a hero or heroine who tries to stop the monster if it's a horror - type story. Or perhaps a scientist who created the monster or is trying to understand it.
I'm not entirely sure without reading it specifically, but it might have a central character who is the so - called'monster'. There could also be characters who are either friends or foes of this main character.
I don't know as I haven't read it. But usually in a story about a house, there could be the family members who live there like the parents, children, or an old grandparent.
In many versions of the monster house story, there are groups of kids. Maybe there's a curious and brave boy who leads the exploration of the spooky house. There could also be a smart girl who figures out some of the secrets about the house. Sometimes, there might be a sidekick - like character, a little younger or more timid, but still part of the group. And, of course, there could be an old neighbor who knows something about the history of the house and gives the kids some clues.
I'm not sure specifically as there are many possible Monster House stories. But it could be a group of curious kids who are the main characters. They might be the ones to discover the secrets of the monster house.
Often, the main characters are the hunters. They are the ones who take on the challenges of fighting monsters.
Since it's a 'monster musume graphic novel', there are likely to be monster musume characters as main characters. These could be different types of monster girls like a lamia, a harpy or a slime girl. There might also be a human character who gets involved with their world and becomes one of the main characters in the story, through which we can see the interactions and developments among them.
Perhaps the main character is a normal person who gets thrust into the world of monster mayhem by accident. As the story progresses, they grow and develop, becoming a key figure in the fight against the monsters. There could also be some mysterious characters that seem to have their own motives and secrets when it comes to the monsters.
The main character is the boy. And of course, there's the monster that visits him.
There might be a young explorer who ventures into the monster zoo and becomes one of the main characters. He or she could be on a quest to discover a rare monster or uncover some secrets about the zoo. And of course, there could be some interesting monster characters themselves that play important roles.