The anti-heroic protagonist of the series and a third mahai angyo onshi from the fallen kingdom of Jushin. Despite the common perception held by Jushin's former citizens that angyo onshi are virtuous and bearers of justice, Munsu usually comes across as somewhat amoral and does not believe in helping people who refuse to help themselves. When he does help others, his methods almost always involve excessive bloodshed, lying, torture, and other questionable acts.
Munsu suffers from a curse that resembles asthma, which can only be alleviated by the inhaler-like charm he wears around his neck. This curse originates from during the Jushin period, where he convinced Aji Tae to switch the curse which was originally suffered by his lover Kye Wol Hyang unto him in hopes of relieving her pain. However, this was ineffective; not only did she die in the end while he retained the curse, Munsu actually fell directly into Aji Tae's scheme. In volume 11, Munsu confessed to Wonsul that despite claims that he was her killer, the truth was that Kye Wol Hyang killed herself by running into his sword while he was holding it right into her heart. He blames himself for her death and believes that he is her killer. When asked by Hong Gildong, he refused to deny that he was her sister's killer although his life was at stake. He went against the entire Hwalbindang after consuming a special drug that removed his asthma for a period of time, and managed to kill most of them. However, the drug had negative side effects when it wore off, and conveniently Aji Tae appeared while Munsu was at his most weak and wounded moment. Seeing his sworn enemy, his condition worsened and he started vomiting more blood, falling into a more critical state. Munsu swears that he will not die despite reality and that he find Aji Tae in the end.
Before passing out, he asks Bang Ja to use an acupuncture needle in his pocket in order to prevent his death, but as soon as Bang Ja did it, Munsu's heart stopped beating. Everyone lost hope and believed that he was dead; however, after a few days despite the humid weather, Munsu's body did not decay. Later it was discovered that the needle contained mandrake extract and Munsu was affected with the infamous hallucinogen, allowing him to escape death. But being effected by the mandrake's poison means he will forever live in a fake world of his most desired dreams. Volume 11 shows the most treasured moments in Munsu's life and more about his past.