Delurking too, because I simply have too many mixed feelings about the ending as well.
All I know is, I AM attached to So Bong. They're the one I watch and cheer on for the past 19.5 episodes from the first time they wake up in So-yong's body. So, heck, yeah, of course what's most important to me is So Bong's happy ending.
And I'm not convinced that's what happen.
I think I'm just bitter because the writers don't explain properly WHY Bong-hwan's soul goes into So-yong's body. What connects them? It is implied that they're both on the verge of dying in the lake, but, th