Across the virtual realm of SE.RA.PH, Masters of digital magic commanded their Servants, great heroes and villains of history and lore, to fight in the Holy Grail War. The prize was the "Holy Grail" itself — aka the Moon Cell Automaton, a lunar supercomputer with the power to grant any wish.

Though the war has ended, with the Servant Nero and her Master on top, all is not well. Not only is Nero's rival Servant already leading an uprising, but a new challenger waits in the dark, ready to tear through reality itself to strike at her heart.

Nero prepares to defend her new throne. Beside her stand her Master and a few loyal allies. Ahead lies not only an ocean of enemies, but an ancient secret far more terrible than any war…