Set at the end of the Heian period (794-1185) and in the early Kamakura period (1185-1333), the series depicts the struggle for power that took place during the Genpei War and the birth of the Kamakura Shogunate, with Hojo Yoshitoki, the victor and founder of the Hojo Tokumune family as the protagonist. The "13" in the title refers to the nobles who made up the "Council of Thirteen", a system of collective leadership established after the death of Minamoto no Yoritomo.