Japan, 1868. The Boshin War is about to break out. The Templars have infiltrated the Emperor's closest advisors and push the sovereign to launch an attack against the Tokugawa Shogun, who is supported by the Brotherhood of Assassins. Is the glorious era of the samurai almost over? 16-year-old Atsuko grew up in the affluent areas of the city of Aizu in the shadow of her brother Ibuka. Destined for an arranged marriage, the girl hides a secret: she can wield weaponry just as well as her brother, whose skill with the blade hides an insurmountable fear of combat. When war breaks out, Ibuka must set off to fight alongside his father. Defying the tradition forbidding women from joining the army in order to protect her brother, Atsuko secretly joins up in disguise, desperate to prove her skills. But faced with plots that go far beyond them, will the strength of the siblings' bond prove strong enough?