In this question, we are not told which story we are referring to. Therefore, we cannot answer that section of the prompt. Nevertheless, we can try to answer the rest of the question.
It is true that we cannot have heroes if we do not have monsters. This is because, in most stories, heroes are only heroes because they successfully face monsters. Monsters are usually the embodiment of evil, while heroes are the embodiment of goodness and courage. Because of this, the two of them exist as an indivisible dynamic in a story.
