I think the writer is never going to appear. I don’t think it’s who you guys think either. Why? Cause that character made himself into an unfavorable position in Kyung’s life, also putting him with an abusive, bias father? If so, major plot holes.
On the other hand, I don’t think “Trumpet Creeper” was meant to be happy. Maybe the writers intended it to end in tragedy. The ‘Trumpet Creeper’ is special to Dan Oh and Haru. The name also implies cheating... I.e ‘creeper’ as in creeping over the wall, a play on the idiom “jumping over the wall” in Asian literature to mean cheating with the neighbour.