About ten years after the Fifth Holy Grail War, Lord El-Melloi II visited Fuyuki City and joined forces with the head of the Tohsaka family to completely dismantle the Great Holy Grail. After a great commotion comparable to the Holy Grail War, the Great Holy Grail was disintegrated. The Holy Grail War in Fuyuki City has come to a complete end here. But it also caused complete chaos in the world's timeline, triggering the worst disaster in history.
But the Holy Grail of Fuyuki City appeared in another land with strong spiritual veins deep in the ocean ten years after the end.
We call this: The Battle of the Holy Grail Rebirth. And this battle of rebirth is the battle to end all disasters.