Yi-Mae shows up out of nowhere to side with and aid the less-than-enthusiastic Yu-Jin in becoming the next King of the Chachaoongs. He claims to be the Yi-Mae Tal who mysteriously vanished two years prior to the start of the story. A ferocious and powerful fighter, he is feared by many and has been given the nickname "Monster Yi-Mae". It is said that Yi-Mae's true face is known only to Jack, as Yi-Mae has never taken off his mask.
He wears a flowing, traditional white robe and has long, flowing black hair, which gives him an androgenous appearance. Yi-Mae is shown to care very much about his appearance (though not to the level of narcissism), or disprove of others based on their appearances - which serves to spark his general dislike for Mu-Young.He wears the mask of the "foolish servant" and he rarely takes it off, so that very few (possibly none outside of Jack) had seen his face. Later, he appeared before the awakened Yu-Jin without his mask. More recently, he removed his mask while speaking with Eun-Yul, then later returned from an excursion and had another conversation with Eun-Yul while wearing his mask on top of his head like Sae-Ha.
When Yu-Jin is in his awakened state or when he is partially awakened, a disfiguring scar appears on the left side of Yi-Mae's face and body. Exactly what the connection between his scars and Yu-Jin's awakened state is, is unknown.
Yi-Mae tends to be incredibly blunt and straightforward, making it very difficult for others to argue with him or extract any information he does not wish to share. He lacks subtlty and usually doesn't bother trying to hide if he's changing the subject or avoiding a topic. When challenged, he does not hesitate to reveal his sadistic and impatient side, often making threats or taunting his opponent. He has a dry sense of humor and his jokes often confuse or infuriate others. Even so, Yi-Mae is a quiet loner that rarely shows any emotion. Mu-Young does not trust him because of this, saying that "You do not know what he is thinking." It is also revealed however that he is not very likely to take the life of anyone, Human or Chachaoong, and he can show grudging kindness at times. Like many of the Tals, he is extremely eccentric and subject to violent changes in mood depending who he's dealing with; the general consensus is that he is not someone that anyone wants to cross.
Like most chachaoongs, Yi-Mae is capable of materialization. His weapon in free-form seems to vary. However, when attacking he tends to prefer a fusion materialization of his left arm. As a Tal, Yi-Mae is one of the more powerful chachaoongs. His nick-name "Monster Yi-Mae" seems to be more due to his ruthless nature than any overwhelming power, as there are several people who have shown themselves to be as strong (or potentially stronger) than him. Nevertheless, his true strength however has yet to be revealed since he generally avoids conflict. Should others attack him, he will usually stick with defense. He is very capable of aggressive as well as defensive materializations. Even though he favors fusion type, he efficiently and easily materializes a sword.
- It is implied that Yi-Mae once had a yongma, but where it went or even if it is still alive is unknown
Yi-Mae's past remains a mystery even to most chachaoongs. He disappeared for several years, and was even thought dead by some. The situation that led to his disappearance is unrevealed, but is hinted to be related to Be-Gak, whom he utterly detests. When he returns, there are many who are unsure (at first) that he is who he claims to be, though he quickly lays those concerns to rest with his ruthless way of fighting. Though he certainly seems to have deep connections with Yu-Jin's past self, he is overtly attempting to keep the truth from the current Yu-Jin for the time being.
(Major spoilers beyond this point)
Recent Korean chapters have revealed this "Yi-Mae" is the yongma of the real Yi-Mae.