Prior to the events of the story, the Longinus Dreizehn Orden, a group of sorcerers, perform a ritual in Berlin during World War II, using the lives lost in battle as a sacrifice for their spell. After the war ends, they disappear, but are rumored to return. In present-day Japan, Ren Fuji is released from the hospital after recovering from a brawl with his friend Shirou, when the Longinus Dreizehn Orden returns. Source: Wikipedia, "[en.wikipedia.org/wiki/Dies_irae_%28visual_novel%29 Dies irae (visual novel)]", available under the CC-BY-SA License.