Jagyum Yu is the Chief State Councillor of GaGook. He is a close associate of the Queen Mother YonRi Yoon, although their relationship is less than friendly. He seeks even more power by trying to arrange a marriage between his daughter Danah and King JinWon.
He seeks power, and is willing to manipulate even the Queen Mother to get what he wants.
Ten years ago, Jagyum Yu comforted his dying wife, who was asking for their daughter. He assured her that she would return soon with the nurse who has gone out to retrieve her. When the nurse returned without Danah, he told his wife to hang on a little longer, while seething in anger about his daughter's disappearing act. When Danah finally returned home with a medicinal herb, her mother had already passed away. Jagyum Yu, full of grief, angrily slapped his daughter across the face and told her that her mother waited for her until the end.
During King JinWon's meeting with his ministers, he interrupts their talk of aid to refugees and increasing the military budget by calling for the Councillor and asking if he knows about the Butterfly. The Councillor is confused, so another minister asks if he is referring to the courtesan. When the king gets up to leave, the Councillor informs him that they must increase taxes by 10% in order to increase the budget, so the king tells him to just do it. The ministers look upon the departing king with disdain.
During a meeting with the Queen Mother, the Councillor discusses the people's support of the Crimson Moon and their own inability to capture him. He informs her that the royal soldiers have executed everyone in the villages that were visited by the Crimson Moon, and that he will likely lie low to prevent the deaths of more innocent people. The Queen Mother scoffs at the idea since the Crimson Moon recently sent them the head of one of their councillors. King JinWon walks into the meeting and asks if the rumors are true that the Crimson Moon is Crown Prince JinYon, then adds that he thought the Councillor or his mother had already killed him. They both are shocked at the accusation, and JinWon plays it off as a joke. As JinWon leaves the meeting, he orders the Councillor to arrest and execute the Crimson Moon.