Physical death doesn't necessarily mean true death when one's memories can be stored outside the body. Memories can be stored in a data bank, and transplanted into new bodies. Memories can be traded, altered and stolen. Society becomes a stagnated, powerless mess.
One day a man, Kaiba, wakes up in a broken room. He has no memories, only a pendant with a picture of an unknown woman. Outside of the room are grotesque floating electrical clouds of disjointed memories. Kaiba is suddenly assaulted, and escapes into space. He travels to various planets, encountering various people and retrieving his memories. Memories of an inconsistent and decaying world, of his own agony and of Niero, the woman in the picture.