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Soonins blood is toxic to vampires but doesn't kill them instead it makes them weaker and notice how Sooin realized that Chiwans blood had a sweet smell to it? But vampires can't have sweet smelling blood cause it's usually bitter with a gross smell. Meaning Sooins blood weakened Chiwans power so much that he had turned back into a human. I assume this wouldn't work if he was born a vampire (I know it's not possible because all vampires were once humans) because he wouldn't have anything to be lowered to once he lost all his powers.
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I think that between drinking lots of Sooin's blood (which suppressed Chi-hwan's vampiric abilities) and losing lots of his own blood (which weakened his power more) Chi-hwan was temporarily more human than vampire. I think this is why his blood smelled good to Sooin and how Sooin was able to make Chi-hwan his link.
Ok that was a little dramatic but we are here for that. NOW, WTF JUST HAPPENED????
I understood but I didn't. How did they safe each other again? chiwan is human now, but how? I wasn't aware of the whole transferring thingy and did that work... ok I guess I'll just be happy it has a happy ending but why did blondy disappeared when chiwan wasn't even dead ok im dumb ╮( ̄▽ ̄)╭