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Seto, a boy who was born when humanity and mankind was wiped out by a project called The Glass Cage Project.  Seto lived with and was raised by his Grandpa who perishes when the game starts.  Left alone in the world, Seto traverses through the abandoned ruins of Tokyo in hopes of finding another living human being.  He meets a silver-haired girl named Ren near the beginning of the game.  He sees her sitting on top of a broken pillar.  Startling her, Ren falls off the pillar and Seto rushes to her side to see if she is alright.  Touching her cheek, Ren gets up and leaves Seto.  After recovering from the shock of seeing another human being, Seto gets up and begins his search for Ren.  Along with his search, he uncovers what happened to mankind itself and he meets and loses the greatest friends he'll ever have.