Seventeen-year-old Koryuun ascends as emperor of the Sokan Empire, inspired by 17th-century China, following his father's death. He assumes power amidst political instability and assassination plots orchestrated by Empress Dowager Kin, who aims to place her biological son, Heitetsu, on the throne. For protection, Koryuun adopts the female identity "Koryuun" and hides among the candidates for imperial wives, sharing quarters with them, including the protagonist Ginga. His sister Tamyūn also joins the wife selection covertly to guard him.

Koryuun possesses naturally delicate, androgynous features and exceptionally long hair, convincing Ginga of his female disguise initially. This concealment allows him to observe the candidates and evade palace conspirators. As assassination attempts escalate, including direct assaults thwarted by Ginga and fellow candidate Kouyou—later revealed as Tamyūn—his true identity becomes known to Ginga and a select few.

When the rebellion led by mercenaries Iryūda and Konton advances on the capital, Koryuun's peril deepens. After rebels breach the palace defenses, he commits suicide as a final act to ensure the escape of Ginga, the other wives, and palace staff. Prior to this sacrifice, Koryuun and Ginga share an intimate encounter in a stable, resulting in Ginga's pregnancy. Their son, Kokuyoujuu, is born posthumously and eventually becomes emperor of the Kan Kingdom.

Throughout these events, Koryuun evolves from a concealed, passive figure dependent on protection into a decisive leader who values others' safety above his own survival. His bond with Ginga shifts from hidden camaraderie to a genuine emotional connection, culminating in their physical union and his enduring legacy through their child.