For 500 years, the Taboo Emperor, Arthur Gaz, ruled the Gaz Empire with an iron fist and conducted inhumane experiments on his own people. However, his reign ended five years ago, when mighty warriors—later known as the Eight Heroes—defeated him in a battle for the capital. His death brought an end to the 300-year-long war between the Gaz Empire and the alliance of six nations. In the present day, Tooru Acura is a former saboteur from the war who struggles to settle into the peaceful world, as he cannot find a job where he can put his fighting skills to use. An opportunity arises, however, when he meets a white-haired Wizard named Chaika Trabant. With a coffin on her back, she is searching for the scattered remains of her father in order to give him a proper burial, and she hires Tooru and his adoptive sister Akari to help her. However, the six nations alliance, which has now formed the Council of Six Nations, dispatches Albéric Gillette and his men from the Kleeman Agency to pursue and apprehend the late Emperor Gaz's daughter—Chaika. With the shocking revelation of Chaika's identity, the Acura siblings must choose between helping her gather the remains of the tyrannical emperor and upholding the peace the continent strives to maintain.