Set in 1635, 35 years after the Battle of Sekigahara, Japan appears peaceful. But a monstrous creature called 'Gun-kyo' that devours humans disrupts this calm. The shogunate burns down villages where Gun-kyo appears to hide the truth. Orin, a former ninja living quietly with her stepdaughter, is drawn back into battle after encountering Gun-kyo while seeking medicine. Meanwhile, Shiro, a Gun-kyo who retains human consciousness, sets out to uncover his origins and the creature's secret.