Each Holy Grail is in effect a mass of pure Magical Energy, which reacts to the wishes of the one who holds it in order to grant them; however, on their own they are not capable of generating true miracles without outside intervention. This Holy Grail has been corrupted after in the 3rd Grail War it absorbed Angra Mainyu, all the world's evil. Any wish will be turned destructive, world peace? Just kill everyone. Wanna be the richest? Kill everyone so you're the only one and the richest. so on