The Holy Grail War is a competition that decides the ownership of the Holy Grail through intense battle royale. While there have been many conflicts over supposed Holy Grails in the past, this term refers to those specifically based around Masters, usually proficient magi, summoning Servants, Heroic Spirits brought forth as familiars, and meeting in battle until only one pair is left to claim the Holy Grail.

The Holy Grail War of Fuyuki, also called Heaven's Feel, is a ritual that has been ongoing for two hundred years. Established by the Tohsaka, Matou, and Einzbern families, the Three Founding Families, as a means to reach Akasha, it is currently thought to be only a competition for something recognized as a possible Holy Grail. Seven magi are chosen by the Grail as Masters and, with support from the Grail, allowed to summon seven Servants to do battle. The winning pair is supposed to be able to claim the Holy Grail and utilize it to grant a wish for each of them. Its true purpose is to actually utilize the seven Servants returning to the root as a way to form a hole directly to it.

At the time there was also a serious flaw in this system, As the Grail required the energy of all seven Servants to help activate the Great Grail and open a hole to Akasha, it would mean that all Servants including the victor Servant would have to be killed, and since the Grail can only be held by Servant, activating the Greater Grail, let alone retrieving the Holy Grail, cannot be achieved, as Masters are incapable of doing so without a Servant. This flaw made the Grail capable of only granting wishes to Masters and Servants.

Fifth Holy Grail War

The Fifth Holy Grail War took place in 2004. Kirei Kotomine maintained his contract with Archer from the previous war, and though he was supposed to act as the impartial mediator from the Church, he mortally wounded Bazett Fraga McRemitz and took her Servant, Lancer. While there were various possible scenarios, in Fate/stay night, Shirou Emiya (as shown in Fate), Rin Tohsaka (as shown in Unlimited Blade Works) or Sakura Matou (as shown in Heaven's Feel) emerged as the victor and help in destroying the Grail rather than activating it.

Dismantlement of the Holy Grail

The Holy Grail was dismantled ten years after the Fifth Holy Grail War in the 2010s. Lord El-Melloi II, a previous Master in the Fourth Holy Grail War, arrived in Fuyuki with Rin Tohsaka to set out to completely dismantle the Great Grail. This development was against the Mage's Association's plan of reestablishing it, so the two sides were opposed. It caused great turmoil of the same magnitude as a Holy Grail War, but the end result was the Greater Grail's dismantlement. This caused a complete conclusion for the Holy Grail Wars of Fuyuki.

Procedure

The Great Grail requires sixty years in order to amass enough mana to summon Servants, making the planning period span over generations. If the Grail is unable to utilize its energy, that which is leftover can reduce the time to as little as a decade, such as in the case of the period between the Fourth and Fifth Wars.

The Servants can be summoned in advance as well, but more than two months, such as in Berserker's case, is an anomaly. They can be summoned far away from the site of the ritual, allowing them to be initially summoned in Europe and then brought to Fuyuki. While played off as only a battle royal where the winner is granted a wish, the real point is to fill the vessel of the Grail with the souls of all Seven Servants. Defeated Servants revert to being pure energy and, while the would normally disappear from the timeline by returning to the Throne as information for the true Heroic Spirits, the Grail stops that process temporarily and collects them.

It is possible to make a wish upon it with only the power of five Servants, allowing it to grant most wishes. It is still incomplete, and will take at least six to bring it into form. Its true purpose, opening a hole to the Root, requires all seven Servants. Once the vessel is filled, the energy of the Heroic Spirits returning to the "Throne" is used by the Great Grail in a ritual to open a "hole" leading to Akasha. Due to the corruption of the ritual, most wishes will require great destruction. Kiritsugu Emiya realized the Holy Grail had been corrupted when it presented him a revelation of how it would grant his wish - instead of saving humanity, it showed him a utopia would exterminate all of humankind besides him, his wife, and his daughter; as a result, Kiritsugu rejected the Grail and attempted to destroy it. Within a decade his adopted progeny Shirou would complete this mission and ensure the malice within the tainted artifact would never threaten the planet again.

Supervision

The First and Second Wars went unsupervised, but the chaotic Second Holy Grail War caused them to rethink the position. Japan had been in its period of civilizing at the time, so the possibility of witnesses spreading the serious damage occurring needed to be controlled even in such a remote area. It is a conflict between magi, so there is no one in the Mage's Association suitable to act as a mediator because of the political implications. They instead sought out the Church, enemies to the Magi, an external authority, and, as it utilized the name of the Holy Grail, one of their most sacred artifacts, it was not possible for them to let its name be used lightly.

The Church acts under the pretense that they cannot ignore the possibility that it actually is the cup that received the blood of Christ, but they already know that it is not related to it. They still send a supervisor because it is too powerful to ignore because they didn't want someone to use the Grail for their selfish desire. They are not concerned about Magi reaching the Root, but someone affecting the actual world is too large a threat. They wish to instead guide a magi seeking the Root towards victory to keep such a possibility from happening. The Association also expresses a measure of interest in the ritual, so they dispatch Bazett Fraga McRemitz to participate in the Fifth Holy Grail War.

The Holy Grail War is unknown to the general populace. The Church is responsible for the cover up work in which they manipulates information by modifying the memories of victims and covering up the battle damage while the Mage's Association handles the media. The Association has the Einzberns cover the cost of any collateral damage. They will punish the landowner should it get too out of hand, such as in the Heaven's Feel scenario. The damage it causes in society and the assassination of Bazett are blamed on Kirei Kotomine, but the activation of the path to the Root gets Rin Tohsaka into a great deal of trouble. Such rituals are only supposed to be done under their supervision, but she also heard they wished to truly execute her because the path was closed even though they succeeded.