A young boy who ends up in the U.S. after the 1871 Shinmiyangyo incident returns to Korea at a historical turning point and falls for a noblewoman.

Mr. Sunshine centers on a young boy who is born into slavery but after a traumatic event escapes to the United States during the 1871 Shinmiyangyo (U.S. expedition to Korea). He returns to Joseon later as a United States Marine Corps officer. He meets and falls in love with an aristocrat's daughter. At the same time, he discovers a plot by foreign forces to colonize Korea.