As punishment for their crimes and sins, the souls of the reckless and cruel were cast down into the dark depths of Hell when they died. But as the numbers of Hell grew, so did its power. Threatened by this, Heaven made a truly heartless decision: That every year, they would send down an army, an Extermination, to ensure Hell and its sinners could never rise against them.

So many souls are slaughtered each year, but many sinners and demons survive by taking shelter during the Extermination. But one day, as one damned sinner made their way out of hiding, they came across a shocking discover — an Exorcist that had gotten left behind after the Extermination, now trapped in Hell.