Summary
Choi Si-woo, a boy struggling with his weight, spends his nights running tirelessly around his neighborhood. One night, while on a late run, he encounters an old man along a forest trail. Before he can react, the man throws a large straw backpack over him, transporting Choi Si-woo to a vast, decaying traditional Korean house (hanok).
As he stands bewildered in the courtyard, he notices numerous dark, ominous figures surrounding him. The old man explains that every 666 years, a ritual is held to choose the new King of Yokai, and each Yokai has a special entry ticket to participate in this ancient competition.
Choi Si-woo learns that he is not entirely human; he is a hybrid, carrying the rare bloodline of a long-extinct goblin clan. Among all the Yokai, only he possesses the coveted entry ticket. Thus begins the adventure of Choi Si-woo, a half-monster boy destined to navigate the dangerous and mystical world of Yokai.