I think it’s also possible that the soul is not Hwal’s soul but is Dark Hole’s soul. Hwal only stole the soul when he stabbed Dark Hole in the past life(even before the 600yrs).
So in this, it means the soul inside Present Sang Woon is Dark Hole’s weakness.
—>Dark Hole wants to kill Sang Woon because he wants to remain as Bulgasal forever, get rid of his weakness and the possibility of becoming a human again.
This also leads to the answer why Sang Woon hated Hwal 600yrs ago. It’s because Hwal was the reason Dark Hole was created(?).
But these conclusions can’t answer why/how Hwal had the soul and got reincarnated. Also the why Bulgasal Sang Woon existed. Maybe Sang woon became bulgasal because her soul was taken from her too or because she gave her soul to her twin sister so that she can live? I dunno xD.
But I got really shcoked at the part in EP6 - Hwal’s dream where Sang Woon almost killed Hwal to make us remember the curse she gave Hwal. XD I got even more confused.
It seemed like she really has deep hatred for Hwal . She looked like a person staring at the murderer of someone Sang Woon cherished. HAHA