Humanity's foundations were destroyed by the Mage King Solomon in A.D. 2016. Nevertheless, the Chaldea organization had foreseen the looming disaster and pledged to safeguard humanity's future. Their mission was to amend the Singularities in history which had been caused by scattered Holy Grails across time and space through Operation Grand Order. Relying on Rayshift time travel technology, Ritsuka Fujimaru and Mash Kyrielight, the final Chaldea masters, successfully resolved six Singularities and now commence their most dangerous mission thus far. Their objective is to defend B.C. 2655 Mesopotamia, a civilization that exists in the Age of Gods, where Rampaging Demonic Beasts endanger humanity. Uruk, the last defense against the beasts, is under King Gilgamesh's control. He sought the help of Heroic Spirits and became a mage. Accompanied by Gilgamesh and summoned servants, Ritsuka and Mash must confront the Three Goddess Alliance, who intend to exterminate humankind. Nonetheless, a significantly greater peril is poised to arise within the city and is preparing to awaken soon.