Following Rentaro's defeat of the Stage Five Gastrea, Tokyo Area returns to uneasy normalcy.
Soon after, the protector of Osaka Area, Sogen Saitake, comes to visit. Seitenshi is forced to act, and Rentaro finds himself drawn ever deeper into events out of his control.
He and Enju will be forced to confront a new kind of threat just to protect the tenuous peace they've won--but how do you fight an enemy you can't even see?