T.C. is the year. 4767. Humanity has been gone for four thousand years since it left its origin, the planet Earth. Mankind, besieged by the hostile extraterrestrial Gnosis, is now rushing to find solutions to fight this existential danger. Shion Uzuki, a Vector engineer, developed KOS-MOS (a customized android with remarkable skills) as one answer to the danger. But when the Gnosis destroys their spacecraft, Shion and her comrades are pushed into the center of a conflict with no clear sides...