To put it in the simplest of terms; The Exalted Grail is a copy of the Einzbern Holy Grail, it is a wish granting device built to pierce into the premade records of everything forever to steal knowledge about how to bring about a true miracle (as opposed to traditional magecraft which is incapable of replicating such a thing.) It is a metaphysical object that gathers the mana in a area and focuses a “beam” into the concepts of the world to allow the winner of the war to reach the “root.” of all things.
Obviously with such great amount of energy almost anything is possible, for a mage with the power to wield all of this power they can do almost anything. Even if they do not desire this miracle that was the original plan of it all, then can grant themselves anything they so desire.
Though rather than being a strict copy, some parts that were uncopyable were stolen from the remains of the previous war, namely that of its core - a artificial human from the Einzbern family - the only family originally capable of preforming this miracle that they lost. This stealing of technology (rather then the moral crime of stealing a body) forced the Delarosa family to flee the wrath of the Einzbern family - the heretical act of trying to create the cup of Christ forced them to flee their Catholic homeland. This small town in Wales was picked for its spirital power, as powerful Leylines (Geographical locations that act as natural magic wells), as a strong source of energy is required to activate the Grail. The presence of Leylines also makes the populace more likely to spring people of magical qualities who in the event that masters cannot be prepared from the family's allies (and enemies) can easily fill the slot of sacrificial lambs. The presence of Heroic spirits is to make sure to fill the cup to its metaphorical brim, to without any doubt manage to pierce reality to the “Root.” Just as the masters these Spirits are fooled with half lies about how this cup can grant any wish. Because it could, but those who fail to reach it shall see their blood fill it to its lip. (For more about servants read the servant entry.)
A copy of the Greater Grail from the previous Heaven’s Feel, the Exalted Grail was built by the Delarosa family based on studies of the remains of the Greater Grail in Fuyuki and at its core are the stolen remains of Justicia Lizreich von Einzbern, the core of the original Greater Grail. This theft is one of the reasons why the Delarosa family had to flee their original Italian holdings, even though the emigration of mages poses a great risk for them. As even the association look upon them with a sour eye, quite possibly the ritual will be crashed by the Einzbern - or maybe they’ll just hang waiting in the shadows to reap the fruits of it instead.
Fuyuki wasn’t a powerful enough spiritual ground to allow the Greater Grail to serve its purpose, reaching Akasha. Therefore the Heaven’s Feel ritual, The Holy Grail War, was created as a means to gather the remaining energy necessary to cast the magic it required.
In that sense, Fuyuki was not the best place to build the Greater Grail in.
Gyfrinach Gwag, on the other hand, most certainly is. As one of the strongest spiritual grounds in Northern Europe with six leylines coming together, the Exalted Grail could have been activated as soon as it was finished.
The Exalted Grail is now situated on a spiritual ground with enough energy to attempt connect to the root... But not enough that success is certain. Due to its experimental nature, and being created by magi who does not fully comprehend that which they were copying, the grail is likely to become unusable after its first activation.
Since the energy provided by the spiritual ground isn’t enough to guarantee success, the Delarosa family decided to further replicate the Fuyuki war. Adding to the Exalted Grail the functionality of the Fuyuki Holy Grail, they thus created a new Grail War.
The energy of the sacrifices would ensure the successful activation of the Exalted Grail, and the prosperity of the Delarosa family or whoever is brave enough to take it from them.