Ryuguheul is Bigak's yongma. Though referred to as pathetic by his master, Ryuguheul quietly and loyally shadows Bigak's every step and is never more than a few feet away from him.


Ryuguheul is a pale, imposing figure draped in flowing black robes. His skin is a ghostly gray-ish white and his hair short and white.  His irises, like with other yongmas, are pale—gray in his case—while the sclera is black. He also has black diamond markings on his face above and below both eyes. He has no arms. He wears long, form-concealing black clothes that have what appear to be black decorative strips of cloth clipped to them, though in actuality, he manipulates these strips of cloths and uses them to fight. The high collar of his robe conceals the lower portion of his face and he is usually depicted as expressionless, rarely seeming to react to things around him.


Taciturn and submissive, he displays less emotion compared to other yongmas that have their own conscience. He appears to be conflicted with his master's merciless nature, but does nothing stop him even when he is the one being hurt. In flashbacks, he is shown expressing more emotion openly by having affection towards small and cute things like birds and children. Ryuguheul has also been shown displaying shock and horror at Bigak's actions, such as when he killed Gabi and Garam.


The only combat ability Ryuguheul has demonstrated so far is the ability to manipulate the cloth clipped to his hair and clothing, using them almost like blades. Though they appear flexible like cloth, they are strong enough to impale people as well as block swords. They are also dexterous enough that he was able to wrap them around Imae's swords and remove them from his body.

Like other yongmas, he appears to heal quickly and easily from injuries that would be fatal to normal people.