"He is haunted... by his friends. All his precious companions and their deaths. Eight years ago, he had friends he cared about very much. Friends he would give his life for. Their names were... Shinya Hiiragi, Norito Goshi, Mito Jujo, Sayuri Hanayori, Shigure Yukimi. But they all died.... Oh, they died all right. And then they were revived.
But the world does not permit the dead to come back. It was a presumption that angered a petty god. The price of their return was great. Very, very great. Can you guess what it was? All the adult humans of the world were killed by a virus. Ever since, Guren Ichinose... has been haunted by that sin and its price."