Choi Kang Chi, born of a human mother and a guardian spirit, is a half-human, half-mythical being raised at the famed Hundred Years Inn. Dam Yeo Wool, a skilled martial artist and daughter of a secret organization's leader, is sent to the inn to protect its master. There, she meets Kang Chi, and despite his true nature, they fall in love. As chaos threatens their world, Kang Chi must restore balance — while Yeo Wool helps him stay true to his human heart.