From the introduction: Tokyo has suffered a supernatural disaster; an Abyssal Darkness has spread across the city, the living vanished, and the dead have come back to life. In the immediate prelude to the disaster, when only certain areas had fallen off the grid, the JSDF deployed infantry, aircraft and tanks into areas stricken with darkness, only to have some of those soldiers have returned as Returned of the Abyss, along with many Dark Beings of clearly supernatural origin like urban golems, trash swarms and fish-ghouls. Somewhere in there the odd Japanese creature of folklore appears as well, but they are clearly in the minority compared to the urban legends. Once the Abyssal Darkness saturated the entire of Tokyo, it started to creep across the rest of Japan, and has now advanced unchecked for years.