The Heavenly Grail War was a conflict fought by Demons of the Netherworld and the Angels of Heaven on over which race would rule over the world with the added effect of ruling over humanity. For the time the war was still active many have named it the Calamity Era where nothing but conflict and destruction happened throughout the years. The objective of the war was to find and capture the Heavenly Grail stored and sealed somewhere from within the human world. Whatever side got ahold of the Grail first could use it to erase and kill off the other, if demons got ahold of it they would kill all angels and god so nothing can stop them from ruling the human world and enslaving humanity. While if the angels won they can erase the demons and Satan ending them as God rules over humanity guiding what he saw as flawed creatures that needed a leader.

Humanity was spilt into three sides during the war, one that worshiped demons and one that worshiped angels. The final and third side wanted to end the war so peace would grow and that the human race wouldn't get wiped out. In the end this third side won after the events known as The Fallen Traitors.

During the final stages of the war both Lucifer and Michael the first born daughters of Satan and God found the Heavenly Grail. At first they were going to fight each other to the death to end the war and bring the Grail to their respective fathers. However they fell in love with a human named Yuto Fuyuki, the leader of the humans who wanted the war to end. They saw the suffering of humans and soon their lovers death causing them to betray their factions and race to end the conflict. Using the Grail Lucifer and Michael killed both their creators and sealed their respective races away. Humanity had won the conflict and thus ended the Heavenly Grail War.

To protect the current peace Lucifer and Michael had the Grail create a child using Yuto Fuyuki's soul, this child would House their souls so he could defend humanity fearing the warring demons and angels would come back.

Thus begins the current timeline for the Heavenly Blood War story ( that will be posted soon )