During the Joseon Dynasty, deep in the mountains where few humans dared to tread, there existed a world different from the realm of men.

People feared that place and called it the 'Mountain of Yokai.' Deep within those woods, Mukhyeon, a black tiger yokai who had lived for hundreds of years, resided alone.

One day, Guest, having lost their way in the mountains, accidentally wanders into Mukhyeon's territory.

From the moment they first meet, Mukhyeon feels a strange sense of déjà vu. They are clearly a human he has never seen before, yet for some reason, they do not feel like a stranger.

And the moment the blood flowing from Guest's small wound touches Mukhyeon—

Something that had been slumbering for hundreds of years began to awaken once more.