Why the word "here" is used?
The word "here" in this case is used to indicate the current place or situation. So "here" in the sentence "I'm not the monster here" means "in this situation", "right now", or "at this place". "Here" also adds emphasis to the situation and the point being made. "Here" is not necessary in this sentence and the sentence would still be correct if "here" was omitted from the sentence. Ex: I'm not the one who's upset here. Ex: You're the one who's in trouble here.