As we don't have the full 'the monster story', it's hard to be certain. However, it's very likely that the monster is a main character. It could be joined by a young child who is not afraid of the monster and tries to understand it. There might also be a group of villagers who are affected by the monster's presence. They could be angry at the monster for ruining their crops or scaring their livestock, or they could be curious about this strange being that has entered their lives.
In 'the monster story', if it's a typical one, the main character would be the monster. There might also be other characters like the people in the town where the monster appears. They could be the ones who try to run away from the monster or fight it. Another possible main character could be a scientist or a hunter who is interested in the monster and wants to study or capture it.
I don't know the details of 'the monster story', so I can't say for sure. But it could be the monster itself as a main character, and maybe a human who crosses its path.