"My Kingdom" is set in the late 14th century, a transitional period from the late Goryeo Dynasty to the early Joseon Dynasty, when people sought power while protecting their beliefs. Yang Sejong ("Romantic Doctor Kim," "Temperature of Love," "Thirty Still 17") plays Seo Hwi, a fighter who never compromises in the face of injustice. Seo Hwi's friend Nam Seon Ho is played by Woo Do Hwan ("Save Me," "Mad Dog"). Seon Ho works hard to pass the military exam and change his social status, but he and Seo Hwi come into conflict due to a misunderstanding.