Previously, Jang Wook was flogged for misplacing a Songrim spirit badge and was also banished from Songrim. As a result of flogging his energy gates opened, which made him feel suddenly hot and cold in an instant, Mu Deok told him if he could bear this sudden change in his body temperature, then he would be able to make this energy his own. She also helped him bear this and eventually he was successful.
Daeho’s Crown Prince came to retrieve Naksu’s sword from UK, which he agreed to give him, but the Crown Prince also asked for UK’s father’s sword, which he refused to give. After hearing no, the crown prince proposed a fight bet, with the winner receiving the sword. UK accepted the bet and agreed to fight with him but he couldn’t stand before the crown prince because of his poor fighting skills. So Mudeok helped UK win the fight by throwing dirty water on the crown prince, which made him cross the line that he had created.
Eventually, the crown prince accepted his defeat but decided to punish Mudeok for throwing dirty water on him. As soon as he took his sword to behead Mudeok, UK immediately protected Mudeok by breaking the crown prince’s sword. After doing so, he realised that he was able to unsheathe his father’s sword. The energy inside him suddenly surged in his arm and made his arm uncontrollable.
He visited Jung Mu to show that he was able to unsheathe his father’s sword. Jung Mu asked him to remove the chain from his hand, which was there to control his arm. As soon as he removed the chain from his hand, he stabbed Jung Mu in his chest because his hand got uncontrollable again. Jung Mu also learnt that UK fought with the Crown Prince, so he punished Uk for doing so by locking him up.
Later, Jung Mu went to see UK and asked him to learn trade and do business, but UK refused and told him that he would follow in his father’s footsteps. At this, Jung Mu told him that he was not his father’s son and was born out of his mother’s love affair, which made UK lose his desire to learn spells.
At the end of Alchemy of Souls Ep 4, as per Mudeok’s plan, the Crown Prince side challenged Jang UK to have a fair fight with him. Taking this as an opportunity, Mudeok fled with UK to the village where she lived to train him.