Yuko and Eri are two normal girls who are sucked into the alternate world filled with tiny people. The people of this mysterious world sees them as their "Great Protectors" who can protect their land in a time of strife. The two girls set out on a mission with a group of warriors from the village to find out how they were brought here and how might they return home. However, there is a war brewing and these two Great Protectors are the political tool that every faction lusts for to rally the people to their side.

In a Holy Grail War, Mages (Masters) and their Heroic Spirits (Servants) fight for the control of the Holy Grail—an omnipotent wish-granting device said to fulfill any desire. Years have passed since the end of the Fifth Holy Grail War in Japan. Now, signs portend the emergence of a new Holy Grail in the western American city of Snowfield. Sure enough, Masters and Servants begin to gather... A missing Servant class... Impossible Servant summonings... A nation shrouded in secrecy... And a city created as a battleground. In the face of such irregularities, the Holy Grail War is twisted and driven into the depth of madness. Let the curtain rise on a masquerade of humans and heroes, made to dance upon the stage of a false Holy Grail.