The Eternal Night Clan had stolen the power of immortality.
As punishment, they were shunned by the living and abandoned by the gods.
Even with eternal life, they could only exist in darkness, living a life of solitude.
In order to better sustain themselves in their ancient castles, the Eternal Night Clan began creating kin and servants by granting their blood to certain living creatures who craved immortality.
This transformed them into long-lived members of the Blood Clan.
The cost of this extended lifespan, however, was a dependency on blood, also known as bloodlust.
The Blood Clan began preying on humans, earning themselves the name "vampires."
People believed that all members of the Blood Clan drank the blood of living creatures.
Of course, Fang Hao didn't know any of this; he couldn't tell which vampires fed on blood and which ones didn't.
In the shows he had seen, vampires always drank blood.