Mr. Sunshine centres around Eugene Choi (Lee Byung-hun) who was born into slavery in Joseon, but escaped to the United States after the 1871 Shinmiyangyo (U.S. expedition to Korea). He becomes an United States Marine Corps officer and returns to Joseon for a mission.
While in Joseon, Eugene meets and falls in love with an aristocrat's grand-daughter, Go Ae-shin (Kim Tae-ri), who is part of the Righteous Army. However, their love is challenged by their different classes and the presence of Kim Hee-sung (Byun Yo-han), a nobleman who has been Ae-shin's betrothed since childhood. Eugene also encounters Goo Dong-mae (Yoo Yeon-seok), a ruthless samurai, and Kudo Hina (Kim Min-jung), owner of the popular "Glory Hotel" where Eugene stays. At the same time, he discovers a plot by the Empire of Japan to colonize Korea and soon becomes embroiled in the fight for Joseon's sovereignty.
I. Historical background
Unlike most Sageuk dramas dealing with the Japanese occupation of Korea, Mr. Sunshine takes place before the Japanese annexation of Korea, in the late 1800s to early 1900s, with a heavy focus on the Righteous Army. Real-life historical events such as Shinmiyangyo, the Spanish-American War, the assassination of Empress Myeongseong, the Russo-Japanese War, Gojong's forced abdication, and the Battle of Namdaemun are portrayed or mentioned.
Historical figures such as Emperor Gojong, Ito Hirobumi, Hayashi Gonsuke, Yoshimichi Hasegawa, Horace Newton Allen, and the Five Eulsa Traitors appear as recurring characters, with others, such as Theodore Roosevelt, Ahn Chang-ho, Eum Sun-heon [ko], Park Seung-hwan [ko], and Frederick Arthur MacKenzie, also making cameo appearances.