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Prologue, Day 3
A hero that becomes eternal in people's minds is no longer human after their death, and is promoted to another form of existence.
Humans who bring about miracles, save people, and achieve great deeds, are called heroes even after their death.
After being so called, they are promoted to heroic spirits after their death and become guardians of humanity.
It doesn't matter whether these people existed in reality or only in myths.
It is people's conceptions that create a hero.
People's wishes that "this is how things should be" give them form and set them up as real.
Authenticity does not matter.
They can have form as long as they have fame as a legend and people have faith.
The ultimate ideal humans have created, the greatest specimens of humanity.
These are the heroes, the heroic spirits.
And of course, since they are beyond human, they cannot be controlled by humans.
A magus usually borrows their power only to mimic them.
They can't summon the heroic spirits themselves.
But the Holy Grail made that impossibility into reality.
It summons the heroic spirit, beyond human control, and turns it into a familiar obedient to the Master.
That nonsense is proof that the Holy Grail is almighty.