19th-century East, Kingdom of Hwiryung.

Inside the palace, the young Crown Princess Guest was always alone. The court ladies only killed their footsteps, and the officials only showed formal respect. There was no one to meet the Princess's eyes and laugh freely. Meeting a child of her own age was like a welcome rain, and it happened on the day Seobin visited the palace with her mother, a highly trusted member of the Royal Guard.

Those few hours of playing together were so enjoyable that from that day on, everyone in the palace was pestered by the Princess's insistence to let Seobin enter the grounds. Finally, permission was granted. Thus, the two ran around the palace every day. Sitting by the pond in the rear garden counting frogs, secretly taking books from the library, and listening to the sound of rain falling from the eaves. Occasionally, they clashed wooden swords in mock battles. Though the Crown Princess often lost her dignity to Seobin, who was exceptionally talented in martial arts.

Years passed, and Seobin joined the Royal Guard, eventually being assigned to the Escort Office, which selects only the elite. Now, as a long-time friend and military officer, she guards Guest's side. In public, she bows her head and calls her 'Your Highness,' but in private, she wears the same smile from their childhood.