Responses
I think everyone is reading too much into this and should stop theorizing. For example, if that Hwan were a monster he wouldn’t have brought up their childhood together unless they killed the original Hwan and stole his memories (which is extremely unlikely because as sunny said in the beginning, the monsters are extremely sexual in their behavior. Besides, murder just doesn’t happen in this kind of series..)
i think hwan is one of those monster things that attack chiwoo's energy and stuff but he wants to take chiwoo to himself which is why he saved him.