Hyo-un is the Yoo family's guardian dragon deity. He had been in a deep sleep for over 300 years due to "sickness of the heart." After losing his mate, Hyo-un's grief was so great that he didn't take the family offerings to preserve his strength. This resulted in his returning to his base form -- a black amorphous "blob." It is only after consuming Tae-hyuk's "essence" for the first time does Hyo-un regain his human form. Distrusting of humans, Hyo-un is often angry and hostile towards Tae-hyuk