Unwillingly thrust into a war-torn world, high school student Mikoshiba Ryouma uncovers his summoner's true master—the O'ltormea empire with sinister designs. Drawing upon his martial arts mastery, he carves a bloody path to escape, striking down key imperial figures in the process. His fortunes change when he rescues two magic-wielding twin sisters from ruthless thieves. Grateful for their liberation, the sisters swear fealty as his devoted retainers, igniting Ryouma's ruthless rise toward absolute supremacy.