A story that takes place from 1998 to 2021.
In 1998, in a world that seems on the brink of disaster, two people aged 18 and 22 meet for the first time but end up hurting each other at ages 19 and 23. At 20 and 24, they learn to trust each other, and at ages 21 and 25, they start to fall in love.
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.