In 1863 Edo, Izuminokami Kanesada and Horikawa Kunihiro undertake a mission to investigate reports of an impending enemy invasion. Following the lead of Toshizou Hijikata, they assume his swords and are entrusted with protecting history against the Retrograde Army's attempts to alter it. Together with fellow sword warriors, they engage in fierce battles with this mysterious force throughout the tumultuous Bakumatsu era. However, their journey is fraught with challenges, including betrayal and brutality, and they are confronted with tough decisions that could endanger everything they cherish.