In the autumn of 1756, the Kuki clan is found in the mountainous fief of Sanda. It has been relocated from the seashore by the Tokugawa shogunate because of the clan's navy, known as the strongest during the age of civil wars and therefore regarded as a menace to the security of the new rulers. The lord of Sanda, Takamura Kuki, is determined to defend the fief as a land warrior, whereas Umihito Kuki, his younger brother, maintains the pride of a sea warrior and dreams of sailing out to unseen foreign lands notwithstanding the shogunate's isolation policy. Umihito is engaged to Princess Yu, a beautiful and lively daughter of the lord of Tanba-Ayabe fief. Although the match itself was made for the convenience of their families, they have known each other since childhood and are strongly bound by mutual respect and profound love.