Kim Wonsik is jealous of his best friend. 

He is jealous of the fact that his best friend is now living in Heaven. Wonsik is jealous that he's living in Heaven because his best friend is living in a better place than Earth and Wonsik isn't there to be with him. 

Wonsik wants to die too, but he has some much to do in life that wasn't accomplished yet. He made a promise to himself that he will do those things and then he'll join his friend up there and do many things like they used to do before he died. 

The only problem is that his own best friend is not living in Heaven. 

His best friend became a ghost. A ghost that Wonsik can't see. A ghost that Wonsik will never see. A ghost that regrets becoming a ghost because he didn't think twice about the consequences. 

What do you think is worse: Becoming a ghost to see your friend who is still alive or not being able to see your friend for an extremely long time until he dies an old age and walks up the stairs of Heaven to meet you?