No he's not related to the blood demon. He absorbed the ghost thingy and also got acknowledged by the sword.
Or he is really related to the blood demon, I haven't read the novel yet and I'm too lazy to do so.
No, the spirit sword already said it that he never chose any people not related to blood demon and he was about to tell him that he was a blood related to blood demon but enemy came so it's either they're a cousins or sisters....
I hope there's no incestヽ(`Д´)ﾉ
SPOILERS
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"Baek Hye-Hyang is distantly related to Soh Woon-Hwi because her ancestor, Baek Ji-woong was the younger brother of Soh Woon-Hwi's ancestor, Baek Chun-kang. However, both bloodlines were separated for over 15 generations; hence, marriage between their descendants was acceptable"
Wait if he is related to a blood demon or something isn't he also related to the two women by blood? So how come they become his wives? Is this kind of "SWEET HOME ALABAMA" thing?!