Raised by calling his mother and father's concubine, Lady Park, as "Mother."

At the age of 13, he was appointed as the Crown Prince, but it was lonely because there were no external relatives or factions that could support him when he became an adult. The one who filled his loneliness was his younger brother, Lee In, born to Lady Park, his father's concubine. Lee In, whom he cherished so much, starts to become bothersome as he proves to be more intelligent, brave, and politically skilled than himself. The anxiety and fear towards his brother gradually transform into self-blame mixed with hatred through the chaos of the rebellion. Lee Seon comes to believe that all the pain and distress he faced were predestined by Lee In and Lady Park.

The weak king is more attracted to a cunning courtier who whispers sweet words than to a loyal subject who speaks bitter truths. Lee Seon, supporting his maternal uncle Kim Jong Bae, decides to send military aid to the Qing Dynasty to fulfill his uncle's ambitions. After making this decision, he despairs when he secretly sends a spy to the Qing Dynasty through his trusted court lady, vowing to uphold the righteousness for Ming Dynasty against Qing Dynasty. However, when this information becomes known to the Qing Dynasty and war becomes imminent, Lee Seon is in despair.

At this critical moment, Lee Seon makes a fatal decision as a ruler.

(Source: Korean = NamuWiki || Translation = MyDramaList)