Kkok Du, once a mortal man in ancient Korea, is now an immortal reaper, revisiting the mortal world every 99 years to punish human weaknesses. His millennia-long existence has hardened him, cultivating a ruthless disdain for humans. During his latest visit, Kkok Du inhabits the body of a gifted young doctor named Do Jin U. However, his mission becomes intricate when he must perform Jin U's medical duties. In an unexpected twist, Kkok Du encounters Han Gye Jeol, a doctor from a lesser-known school, yet harboring enigmatic powers that captivate him. Are their destinies intertwined from a past life, and why does she wield such influence over him? As Kkok Du grapples with his task, he finds himself increasingly drawn to Gye Jeol, facing a daunting choice: fulfill his duty or risk everything for love.