I agree, I don't think he gives ML vibes but I hardly see how the author could make a romance between Haesu and Eunha. If it does happen, it will probably be a tragedy/bittersweet ending where either Haesu moves on after being happy or wtv and disappears, or maybe they might reunite in death like in some other stories.
I think Haesu was alive a long time ago (we could see a child looking a bit like him when Eunha was in his head) and I think he got sick or something and died and became evil after being a ghost for a while or maybe something happened that turned him this way. I don't think they are two separate beings but who knows?

This was labeled as ‘romance’ but it seems the evil guy just gets attached to the people who invite him. He’s so lonely he becomes obsessed. But i dont get why or how there’s romance in this. Unless he has a super tragic back story that she can somehow get behind and forgive him? After he show her bullies death of course. There’s just a lot of holes in this story lol