The Crimson Curtain (紅蓮の帳 Guren no Tobari ) is the crimson world created by the summoner performing Tenpa Jōsai, the ceremony to Divine Summon the God of Retribution "Flame of Heaven", a True Demon God of the Crimson Realm. It is a world to receive "Flame of Heaven", who can exhibit his powers as a God, as well as a place where the sacrifice who will be compensation for the summoning can be offered.
When the Crimson Curtain is formed, the space within it is filled with a crimson color released from the summoner and becomes heavier. The Crimson Denizen who is to be the sacrifice is fixed in place and their Silhouette of Existence (存在の影法師 Sonzai no Kagebōshi ), which will lead to their death when it is taken in and converted, is forcibly formed.
This interference with the sacrifice progresses along with the summoner's invocation, and Tenpa Jōsai activates when the Crimson Curtain erodes and takes in the Silhouette of Existence and converts it into the "Cor" (
However, though the Crimson Curtain was powerful, it was also a heavy load. At the end of the Great War of the Middle Ages, when Mathilde formed the Crimson Curtain, she suffered through boiling pressure and pain through her whole body. As Mathilde was on the verge of death from mortal wounds, it is possible that the pain she suffered from the Crimson Curtain's load was greater than normal. She had captured Töten Glocke's Jarri within the Crimson Curtain and used him as the sacrifice.