A year before the battle of Sekigahara that ended the Sengoku Period, the ninja Saizou Kirigakure meets the miko Nami Isa as she's attacked by assassins. Her shrine was destroyed by Tokugawa Ieyasu for siding with Yukimura Sanada. Meanwhile, Sanada has been gathering ten warriors known as Sanada's Brave 10, who have the power to change history. As they gather one by one, Nami's own mysterious power awakens.