“The complex of the boy, Choi Si-woo, is being overweight. Choi Si-woo runs and runs around his house until past midnight, and he encounters an old man on a walking trail. In the blink of an eye, the old man covers Choi Si-woo with the straw backpack he is carrying. Where Choi Si-woo had stumbled upon was an enormously wide ruined traditional Korean house (hanok).

At the edge of the spacious courtyard, surrounding him on the courtyard, there were numerous black shadows standing. To the bewildered Choi Si-woo, the old man speaks. Once every 666 years, a ceremony is held to select the king of Yokai and each Yokai in this world possesses one entry ticket for it. And Choi Si-woo is, in fact, a hybrid of a human and a goblin, inheriting the blood of an extinct goblin. Among the goblin folk, only Choi Si-woo possesses the entry ticket. As the sole survivor inheriting the blood of a goblin, the adventure of the half-monster boy, Choi Si-woo, begins.”