Due to the long war, the Muromachi shogunate gradually declined. The world entered the secret land of the mountains and seas in the Warring States Period, which advocated blood debts and blood repayment. Deep in the dense forest of Ki-no-Kuni, there is a gun group with Yatagarasu as its military flag emblem. They are mercenaries and gallop on the battlefield. Their name is "Saigashu". The man who inherited the title of the leader of the Saigashu is named Magoichi, a young man who drifted here from a foreign country. On the other hand, Saburo, who was the first to notice the invasion intentions of the European powers, ran around to protect Japan. The two people who had no intersection at first became connected with the attack of foreign invaders. How will this group of men in the Warring States Period carry out their beliefs and justice? Their story officially begins-!