Celestia, a noble lady from a prestigious family, is told a prophecy by her half-sister, who claims to be the "heroine" of a story. "Dear sister, you will have your engagement annulled and be abandoned by our father. In the end, you'll be sent away to a convent." To avoid this disastrous future that is unwillingly becoming a reality, Celestia decides to apprentice herself to her grandfather, a legendary high-ranking military officer on the frontier! She resolves to live a strong life as a soldier. ...However, for some reason, the Prince she meets at the border starts taking an interest in her!?