This is a Holy Grail War covered in lies.

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