The series tells the story of a woman who remembers her past lives by repeating death and reincarnation for 600 years, and a man who cannot kill nor be killed and has lived for the past 600 years as a Bulgasal—a mythical creature that feeds off human blood and is cursed with "Cursed since birth and exempt from death, a revenge-driven immortal sets out on a quest to reclaim his soul and end a 600-year-old vendetta.