Shion Pavlichenko becomes a Contractor one night as meteors sweep over the star-studded sky. Despite her brother's change, Shion's twin sister Suou has a reasonably normal existence, going to middle school with her friends and dealing with the embarrassment of growing up. Everything changes, however, when a masked guy wrapped in black invades her house, ruining any feeling of normalcy she previously had. Suou, who has been shown to have latent Contractor powers, is caught between family, friends, and her own sense of purpose as she enters the vicious world of cutthroats and spies that Contractors call home.