Responses
I think Daejun always had a gut feeling ... That's why he took Sihyeon to all those places Hajin frequented idk lol
Since chapter 37-40
Daejun knew it since he was drunk and half asleep in early chapter (I can’t remember exactly ). Then, sihyeon said something to him that “let’s think that I’travel somewhere far away forever”. He was uncertain about his suspicion but the sentence confirmed it that sihyeon is Hajin to him.
Sorry i'm kinda lost, since when did daejun know sihyeon was hajin?