Kayo lives quietly with her father in a food and tea house in early Edo-period Japan—until the Princess of Sunpu Castellan asks an extraordinary favor: take the princess's place in a marriage promenade, since they are identical in appearance. Kayo agrees and sets out toward Edo and Sunpu escorted by six samurai. The journey entangles her in supernatural dangers and the secret ritual behind the "Sword Retrieving Imperial Match"—a cover for something involving the legendary five great swords that no one was supposed to uncover.