After being jobless for three years, Choi Joon Woong decides to take his own life and goes to a bridge to jump off of it. However, he finds someone else there who is also about to jump off the bridge and gets into a fight trying to save them. In the fight, the two of them accidentally fall off the bridge. A crisis management team run by grim reapers belatedly arrives at the scene, and Choi Joon Woong ends up falling into a three-year coma with his soul having escaped his body due to an error caused by the grim reapers. Now a soul who is half alive and half dead, he unexpectedly gets a job at the crisis management team at the most prominent company of grim reapers in the underworld. Gu Ryeon is the leader of the crisis management team . His job at the team involves taking special care of people with a high risk of suicide and helping them want to continue living.

Based in Shinmiyangyo, or the U.S. expedition to Korea in the late 19th century, Mr. Sunshine tells the story of a Korean boy born into a family of a house servant running away to board an American warship, later to return to his homeland as a U.S. marine officer. He ironically falls in love with an aristocrat’s daughter and discovers the dark scheme to colonize the country that he once ran away from.