Pure cinema.
Joy being an actual full bore sociopath is honestly so good, maybe im giving pito too much credit but it really feels like a commentary on the ol love triangle protag who just "accidentally" plays both sides for the whole story. Joy doesnt care about how her actions effect others, she just wants things to be easy/happy for her, and isnt concerned with how the poeple she toys with might get hurt. And the way the author hides it all until the last couple of chapters so we think were gonna get a "i can date both of you" ending? amazing incredible peak. All the characters fit so well into overplayed yuri stock characters up until that reveal.
Honestly it is a happy ending though considering Namsu gets to escape from Joy before they get really serious, and the implication that hye-yeon is realizing how toxic Joy is is pretty strong in the last chapter. Not to mention the cover photo changing from the three of them to Joy alone is pretty clear.
What a ride, after my pet i was kinda expecting more weird slop from this author but boy was i wrong