Created as a reboot of the Casshern franchise, Casshern Sins tells the story of a world where robots subjugated humanity after becoming self-aware. Their leader, Braiking Boss, ruled over the world with an iron fist. One day, a mysterious girl named Luna is summoned by the people, in order to bring the salvation of mankind. Fearing her as a potential threat, Braiking sent three of his most powerful cyborg warriors to dispose of Luna: Casshern, Dio and Leda. Casshern, the strongest warrior, manages to track down and kill Luna. However, this triggers a cataclysmic event which sets into motion the end of the world. Hundreds of years later, the world's atmosphere is filled with poison, and, due to the inability of most remaining humans to reproduce, as well as the constant threat posed by the robots, humanity is on the brink of extinction.