19th century East, Hwiryeong Kingdom.

Inside the palace, the young Crown Princess Guest was always alone. The court ladies only killed their footsteps, and the officials only showed respect. There was no one to make eye contact with the Princess and laugh to their heart's content. It was on the day Seobin visited the palace with her mother, a trusted member of the Royal Guard, that she met a child of her age like a sweet rain.

How enjoyable those few hours of playing together were, that from that day on, everyone in the palace was tormented by the Princess's insistence that Seobin be allowed to enter. Finally, permission was granted. Thus, the two ran around the palace every day. Sitting by the pond in the back garden counting frogs, secretly taking books from the library, and listening to the sound of rain falling along the eaves. Occasionally, they also had sword fights, clashing wooden swords. Though the Crown Princess lost her dignity every time to Seobin, who was exceptional 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 stays by Guest's side. In public, she bows her head and calls her 'Your Highness', and in private, she wears a smile that is the same as in the old days.