The film is inspired by the Korean Joseon dynasty Buddhist paintings and early Buddhist scriptures of the "Ten Kings of Hell". In the early Buddhism concepts, the Ten Kings of Hell serve as magistrates of each of the ten courts of the underworld to determine the fate of the deceased including the type and severity of punishment and the course of their cycle of rebirth. On the 49th day after death, the soul of the deceased comes before the seventh king and may be reborn, depending on his or her actions in this world.
The three guardians of the Afterlife, Gang-lim (played by Ha Jung-woo), Hewonmak (played by Ju Ji-hoon) and Deok-choon (played by Hyang-gi Kim) are named after the same three gods of death Gangrim Doryeong, Hae Wonmaek and Yi Deokchun, from the Korean mythologies of Jeju Island. As portrayed in the film and in Korean mythologies, the gods of death carry a "Jeokpaeji", the list with the names of the dead written on a red cloth (in the film, it is a card with red ink); when they call the name of a person on the Jeokpaeji three times, the soul leaves the body, being retrieved from the living world and is then escorted to the underworld by the three gods of death. Also notable in the film is the red ink writing on the Jeokpaeji card; historically in Korean culture red ink was only used to note the names of the dead on the family register. If the name of a living person was written in red ink, it was considered a sign that the person who wrote the name wished harm upon the other. Now, using red ink is a huge 'no' throughout the country, especially to write down a name.