A near future, where humans have been defeated by the viral parasites named Gastrea. They have been exiled into a small territory and live in despair, side-by-side in terror. In this world trapped in darkness— Rentaro, a boy living near Tokyo and member of the "Civil Security"—an organization specializing in fighting against the Gastrea—is used to accomplishing dangerous tasks. His partner is Enju, a precocious young girl...
