What is the Holy Grail War?

The Holy Grail War is a grand battle to the death between seven competitors.  Seven people—usually proficient magi—summon powerful Heroic Spirits, legendary heroes from history or myth.  These Masters and their Servants fight to the death in the Japanese city of Fuyuki, for a chance at reaching the Holy Grail and having their dearest wish granted.

Magus

The term for human practitioners of Magecraft.  Magi are frequently, but not necessarily, descend from old magical families, as affinity to sorcery is something transmitted through blood relations.  Many major families belong to the international Mage’s Association, but the Association is prone to petty power struggles, and has little concern with the Holy Grail War.

The Holy Grail

The Holy Grail is the ultimate prize of the War.  Magi from around the world gather to participate in the world, and seven of them are chosen by the Grail itself to participate as Masters by marking them with Command Spells.  These Masters then summon their respective Servants and begin to fight.  The Grail can only be won by a single Master and Servant, after the other six Servants have been eliminated.  When touched by the winner, it will grant the dearest wish of both the winning Master and winning Servant.

The Holy Grail War itself was established by the Three Founding Families:  the Einzberns, Tohsakas, and Matous.  To date there have been four wars, none of which resulted in a victor.  In the first two wars, the fighting was so chaotic and bloody that there were no survivors, and the Church was brought in to mediate.  In the Third War, the vessel of the Grail was destroyed amidst the fighting, prematurely ending the war.

Ten years ago, the Fourth War almost had a victor, but rumor is that the Grail was once again destroyed before a wish could be granted.

The year is 2005, and the Fifth Holy Grail War is about to begin.

Masters

When an individual is marked with their Command Spells, they become a Master.  Masters are chosen by the Grail itself, usually people with a desire that they want to be granted.  The Grail favors the Einzberns and Tohsakas first, then chooses other suitable Masters.  The Matous also usually participate in the War, but currently have no magi of significant talent left in their family.

Under ordinary circumstances, a Master is always a spellcaster, usually a Magus with a Magic Circuit, who is selected by the Grail. It is possible for an ordinary person to become a Master, though this is rare.  After gaining their Spells, the Master summons their Servant in the months leading up to the war.

A Master’s role is to direct their Servant in combat and provide them with magical energy.  As Servants are unnatural entities, they must subsist off a constant supply of mana or they will vanish. A Master that is providing magical energy to a Servant will "leak" magical energy in a volume that is easily detectable to most spellcasters.

In order become a Master, a person must successfully summon a Servant through use of a specific Formal Craft ritual. Upon completion, the Master must formalize a contract with the Summoned Servant by acknowledging their respective roles.

Servants

Servants are familiars of the highest possible rank, made from Heroic Spirits.  These can be either great historical heroes, or characters from legend that have become famous.  Each of these Heroic Spirits typically has a wish they want fulfilled by the Holy Grail, and have their own motivation for seeking it, separate from their Master. The Master is their source of mana and their anchor to their world, so they have a strong incentive for following their Master’s orders.  However, the only way to force a Servant to carry out an order against their will is to use a Command Seal.

They come in seven classes, each with different skills and weaknesses:

Saber

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Archer

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Lancer

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Rider

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Berserker

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Caster

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Assassin

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Servants can switch between a Spiritual Body, which is invisible and resistant to detection and scrying, and their Material Body.  In their Spiritual Body, they can phase through objects, but they cannot carry anything with them and are limited to spiritual sensations.  Being in Spiritual form also lessens mana consumption.  Berserkers consume much more mana than the other classes, in exchange for its power.

Servants can exist without a Master for a short time, but its mana will slowly deplete.  Once a Servant is out of mana, they essentially die.  However, Servants can seek other sources of mana, with or without a Master.  They can consume human souls for extra energy, or perform tantric rituals to take extra energy from Masters or hosts.  Eventually, though, a Servant must seek out a free Master and make a new contract to have any hope of reaching the Holy Grail.

Those summoned as Servants are given the minimum information required to allow them to fit into any era. No matter how ancient the Heroic Spirit, they should understand a number of concepts that were not known in their time. The knowledge is not all-encompassing, so concepts may have to still be explained to them. They also have the same general knowledge of the Holy Grail War as the Masters themselves. They are granted some knowledge on other Heroes when summoned. Witnessing traits of other Servants can allow them to deduce their true names with the knowledge even if they are from incompatible eras.

The true name of a Servant is something vital to battle, as it can reveal much about them. They most often have their Masters refer to them solely by their class name. Though, there are Servants and Masters with extreme confidence or no filter in revealing their true names for all to hear. Their names can reveal certain traits about their abilities, allowing for specific countermeasures, and there are many famous heroes that had met untimely deaths in life.

When summoning a Servant, a catalyst can aid (or be necessary) in summoning a particular hero.  This can be a sword, a relic, or even part of the hero’s body.

Noble Phantasms

Noble Phantasms are powerful armaments made using the imagination of humans as their core, and weapons or abilities owned by Heroic Spirits. They are the embodiment of the ultimate mysteries of a hero that symbolizes his existence through historical facts and anecdotes. They can be physical weapons, such as swords, lances, and bows, or support items, such as rings and crowns. They can also be abstract concepts, like unique abilities, unique means of attack, curses, and changes to the environment and its physical properties. When summoned as Servants in the Holy Grail War, they are the trump cards of the heroes that allow them to overcome others in battle. Noble Phantasms represent the legends of Heroic Spirit. In other words, it would likely reveal their identity to other Masters if used.

There are a number of Noble Phantasms that display passive abilities that continue to function without any need to call out their names called continuously-active. For weapons that release a great attack, they only reflect their power upon having their true name called, so striking with them as regular armaments will only reflect the physical abilities of the wielder. They each possess a great amount of magical energy that show them being things "outside of normality", miracles exceeding both humanity and magecraft.

Command Spells

These spells, which appear as markings on the Master’s hand, are three claims of absolute obedience.  When used, it will force the Servant to obey a particular order, and may even warp reality slightly to allow the Servant to carry out an extraordinary task (such as teleporting to its Master, or boosting their mana necessary for a Noble Phantasm).  Once used, the Command Spell will disappear.

The Master must take careful consideration on when to use these.  Though a Contract will not end when all three are used, the Master no longer has any means of absolutely controlling their Servant—opening the possibility of their Servant turning on them.  Even if a Master forges a new contract with another Servant, they do not gain any additional Command Spells.

A Command Spell’s power can weaken if an order given is either too vague (“protect me throughout the war”,) or difficult (“win this battle”).  A command such as “Obey my every order from now on” will fail completely, but the Master will still lose their Command spell.

New Contracts

If a Master loses a Servant, they lose their Command Spells. When there is a Servant with no Master (who has died or foreited), the Grail will redistrubute Command Spells to someone that can act as a new Master. The Grail prioritizes those who were previously Masters that lost their Servants, so even Masters that have lost their Servant can still be considered part of the conflict.

A Master without a Servant can make a pact with an unclaimed Servant at will, even contracting with multiple unclaimed Servants (though this is hazardous due to magical energy consumption.) This also means that a Master can claim a new Servant regardless of the length of time since his last Servant.

Likewise, a Servant that loses their Master may still contract with a new Master as long as they remain in the world.  Without a Master giving them mana, they will quickly be drained of energy until death, so they have a narrow window of opportunity.

The Church

In order to ensure that the Holy Grail War does not become an all-out bloodbath, the Church was brought in to mediate the war and ensure strict rules are followed.  The Mediator is there to make sure citizens of the city are not made aware of the Servants and Masters, and that too much collateral damage is done to the city.

The Church—where the Mediator resides—is neutral ground, where Servants are forbidden from clashing.  The Mediator can be sought for guidance and advice regarding the nature of the Holy Grail War and its rules.  Additionally, a Master without a Servant can seek refuge at the church by forfeiting their rights to make any further contracts.