The ongoing war between the Levamme Empire and the Amatsukami Imperium has endured for years. However, amidst the conflict, the Prince of the Levamme Empire has declared his love for Juana del Moral and has vowed to end the war within a year as part of his proposal. But when the Amatsukami catch wind of this announcement, they launch an attack on Juana's residence, determined to assassinate her. To save her, the San Maltilia Airforce hires a mixed-blood mercenary named Charles, also known as a bestado. Charles acquires the responsibility of secretly transporting Juana to the Levamme capital. This mission is not a simple one, as Charles must venture into the danger of an enemy-infested ocean alone. The challenges he faces along the way far exceed anyone's expectations.