The game takes place in a parallel universe to the visual novel Fate/stay night
As of the 2030s, the world's mana was completely gone.
The universe of Extra shares the events of the War fighting for Fate Extra universe until a "certain major incident" in the 1970s
that caused the world's mana to start drying up causes it to split off into its own separate universe.
The world is set in a school called Tsukumihara Academy, a fictional place existing with an artificial environment called the Moon Cell.
There, the Moon Cell orchestrates a replication of the Holy Grail War using a system called Serial Phantasm or SE.RA.PH,
which handles the summoning of Servants.
Servant data is taken from the Automaton,
a spiritual computer system built on the lunar surface by a pre-human civilization and discovered by humans in the year 2032.
The Automaton has monitored and recorded all occurrences on the Earth (including the activities of human heroes) since time immemorial.
In this sense, it is similar to the Throne of Heroes.
Unlike the Fate/stay night counterpart, all involved are either human personalities that function as NPCs,
or hackers, resulting in what Rin herself called a "fair system," as it does not involve innocents.
In addition, Servants are to convey the will of the Moon Cell above their own needs.
Each of the 128 participants in the war must duel the other Masters in a place called the Arena,
where failure results in deletion from the digital world and death in the other.
When only one remains, the "Holy Grail" shall grant the victor's wish.
Waking up in a strange virtual world with no recollection of the past,
the main character finds themselves forced to fight for survival in a war they do not understand for a prize beyond value;
the opportunity to have one’s wish granted.
With only an enigmatic “Servant” by their side,
Hakuno Kishinami will have to face both friends and foes in battles to the death in order to not only gain possession of a mysterious object known as the “Holy Grail,”
but also to find the answer to the most important question of all: “Who am I?”
Let's go to the game War fighting for Fate Extra...