Hachimaru is a sickly boy so frail he cannot survive without life support, passing his days lost in online games. His world cracks open when his robotic pet Hayataro drags home a Daruma doll; once Hachimaru paints its eyes, it springs to life as a cat-like warrior calling himself a samurai. In this galaxy, samurai are cyborgs whose spines are replaced by a memory unit called a key, and Hachimaru may be one of the holders of the seven keys needed to open Pandora's Box and save a dying universe.