After half a day, Sovell had figured out most of the Greater Grail's structure.
Overall, the Holy Grail War's supposed ability to "grant wishes" was a by-product of the immense accumulation of magic power from the ley lines.
Using the enormous amount of magic power collected by the Greater Grail for an equivalent exchange did have a chance of success, provided the user knew exactly how to make their wish come true.
That was how it should have worked.
But the Holy Grail was no longer a simple crystallization of magic power.
Combining what he had sensed near the Greater Grail itself with Zouken Matou's memories, Sovell tentatively concluded that the problem had arisen during the Third Holy Grail War.
During the Third Holy Grail War, the Einzbern Family had broken the rules in pursuit of victory, summoning a Servant of an eighth Class beyond the standard seven-Avenger, Angra Mainyu.
Angra Mainyu was the god of evil and darkness in Persian mythology. In Zoroastrianism, also known as fire worship, he was the sworn enemy of Ahura Mazda, the god of goodness, light, and creation.
His other name was "All the World's Evil."
Yet the summoned Avenger had been exceptionally weak, dying on the fourth day of the Holy Grail War. When the Holy Grail reclaimed his soul, the world's evil within it contaminated the Grail.
As a result, the magic power within the Holy Grail had degenerated into an evil sludge. If anyone made a wish upon such a Grail, it would surely fulfill it in the most twisted way possible.
For instance, if someone wished to become the strongest mage in the world, there were many ways to achieve that.
These included, but were not limited to, turning him into King Solomon, granting him extraordinary insight, or transforming every