In a world reduced to an endless sea of sand, civilization once flourished and then collapsed after a war between beings known as Kagijin, humans who wield the supernatural power of Keys. These Keys, when inserted into a keyhole on the user’s body, manifest as weapons called Kenbui, granting abilities that can rival entire armies. Now, centuries later, the Gabbia Empire has risen, claiming most of the continent through military might and the exploitation of these Keys.

The story begins with Chiruda Portman, a female soldier of the Gabbia Empire, who is ordered by the powerful senate chairman Dejanira Leonidas to track down and execute an escaped death‑row prisoner designated as No. 58. While searching the treacherous Great Sand Sea, her unit is caught in a sandstorm and scattered. Chiruda wakes aboard the ship of a salvage crew, having been rescued by none other than No. 58 himself: a young man named Tsubame.

Tsubame is the brash, rough‑spoken leader of a small salvage team that scours the ruins buried beneath the sand for scrap metal and artifacts. Despite his fierce appearance, he is loyal, kind‑hearted, and cannot ignore those in need. He is secretly a Kagijin, with a keyhole on his right wrist. His Key is called the Dankuu, which takes the form of a katana named Hien‑tou Haru Hayate. Its signature technique, Zettoukuusen, allows him to cut anything from a distance, but the power is exhausting and can only be used twice per day.

Chiruda soon learns that she herself was meant to be killed by her fellow soldier Deneb, a Kagijin who wields the Emperor Key in the form of a flaming axe. With Tsubame’s help, she defeats Deneb and realizes the empire has betrayed her. Together, Chiruda and Tsubame swear to rebel against Dejanira’s tyranny.

Dejanira Leonidas is the true power behind the empire, a seemingly ageless man who has lived for over two thousand years. He holds the Key of Fate and Causality, which grants him immortality by severing himself from the flow of time. He seeks to expand the empire’s control across the entire continent, using Kagijin experiments and military force without regard for human life. He also keeps the young emperor Aldebaran Domitianus Gabbia as a puppet ruler.

Their journey takes them to the border town of Reto, ruled by General Crocket, the “Iron Hand.” He appears benevolent but secretly kidnaps citizens for Dejanira’s experiments. After exposing his crimes, Tsubame and Chiruda fight and defeat him, then infiltrate the imperial capital. Along the way they encounter other Kagijin: Asura, a battle‑obsessed youth wielding the Death Key; Sedile, a cat‑eared soldier who wants only to return to her sister; and many others. Tsubame faces Asura in combat and awakens a new ability, Nino kata – Mutou Kazaguruma, turning the blade of his sword into wind.

Eventually they reach the imperial palace and confront Dejanira directly. The final battle forces Tsubame to push his power to its limits, confronting both the physical might of Dejanira’s forces and the ancient secrets of the Keys. The story concludes with Tsubame and Chiruda achieving their goal of freedom, though the cost is high and the future of the empire uncertain.

Key characters also include Tsubame’s father, Hanza Hurley, the archaeologist who originally unearthed the Keys and was executed for warning of their danger; the salvage crew members such as the flying dolphin‑like creature Air Dolphin; and various Kagijin soldiers and officers who either oppose or join the rebellion. The narrative arcs move from the initial survival and alliance, through the exploration of the sand‑sea and the town of Reto, to the infiltration of the empire and the climactic showdown, all while exploring themes of freedom, loyalty, and the misuse of power.