Kokdu: Season of Deity follows the story of Kokdu, a grim reaper who comes down to the mortal realm every 99 years to punish humans. During his latest descent, he inhabits the body of a human surgeon named Do Jin-woo. While navigating his new life, he encounters Han Gye-jeol, a doctor with mysterious abilities who seems to have the power to command him. As their lives become intertwined, Kokdu begins to uncover the truth about his past life and the tragic curse that has bound him to the afterlife for centuries. The series explores themes of reincarnation, destiny, and the enduring nature of love across lifetimes. As Kokdu and Gye-jeol work together to solve medical mysteries and confront the dark forces surrounding them, they must navigate the complexities of their evolving relationship while fighting against the constraints of the divine laws that govern the underworld.