19th-century East, the Kingdom of Hwiryung.

Inside the palace, the young Crown Princess Guest was always alone. Court ladies moved with hushed footsteps, and officials merely showed formal respect. There was no one to meet the Princess's eyes and laugh freely with her. Meeting a child of her own age was like a welcome rain; 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 that Seobin be allowed to visit. 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 even had sword fights, clashing wooden swords. Though the Crown Princess repeatedly lost her dignity to Seobin, who was exceptionally gifted in martial arts.

Years passed, and Seobin joined the Royal Guard, eventually being assigned to the elite Escort Office. Now, as both an old friend and a military officer, she stays by 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 days.