This is only my thoughts. Im not really sure about this myself but i think if the monsters get killed/ what they desired is fufilled they get reborn. A new self without any desire making them have no emotions as you can see the humans walking around naked and emotionless. It seems that desire is what makes them evil and greedy. Hyun and hyuk gets reborn and is a cacoon, after it hatches we can see a new hyun, emotionless. He wanders and finds the phone of the girl who looks like maria (sorry forgot the name) she wrote a song and he remembered it making him feel emotions (sadness) and bring him to his senses(?). Time has passed and they (the people in the green house) are now safe. It seems that hyun keep looking for them and eventually found them in the end. They live a happy life, fin. I have no idea though about hyuk and what happened to him
They get engulfed into their desire as once they are satisfied and no longer have anymore desires, they get reincarnated to a being with no emotions, no wants, no nothing but Hyun is the only one(?) who overcomed that therefore he was crying (emotions) thats what i feel
Yeah bc he listened to the song on the phone
Does someone have an explanation for the ending? make it as long as you want, I really need one of those ending analysis. Would also be nice if the author said something more about what happened later