Servant

Servants (サーヴァント) are Heroic Spirits summoned by the Holy Grail for the purpose of competing under Masters in the Holy Grail War.

Nature
Servants are Heroic Spirits made into special familiars of the highest rank that are bound to the Master. Pure Heroic Spirits, the "main body" in the Throne of Heroes, can only be summoned by the World, and summoning even one is considered to be a miraculous occurrence. Differing from the normal definition of familiars that can be likened to minor mascots unable to be stronger than their masters, Heroic Spirits are the most powerful of beings with which even the five magicians would never be able forge a contact. Rather than it being a hard process to summon them or the fact that they far surpass magi, it is their intrinsic nature in that they are beings beyond magecraft. Magi can perform rituals to borrow their power to mimic them, but cannot summon actual Heroic Spirits themselves.

Even the Holy Grail lacks the power to summon a true Heroic Spirit, so the process is facilitated by summoning them into one of seven vessels prepared beforehand. The Greater Grail makes a copy using information from the "main body" of the Heroic Spirit, an "emanation", that returns to them as information, in the form of a soul, upon the death of the Servant. Disconnected from the "main body", they are able to know of the actions of the Servant through records, as if reading a book. Due to this, any Heroic Spirit summoned in multiple Holy Grail Wars will lack knowledge of previous summonings. The only exemption is King Arthur due to her unique circumstances.

Similarly as to how demons require a form invented by humans in order to take shape, Heroic Spirits need a form to exist in the world. The vessels, classes, act as their temporary name and method of existing. Acting like a "passport to the present", the vessel prepares them for their role as a familiar in advance, allows them to take on that role to help them take form, and brings them forth into the world. Only heroes matching the attributes of the classes are brought forth, allowing them to be summoned into any reflecting their abilities.

Although too powerful to be controlled by humans, they are bound by three Command Spells, representing the Masters' "right to rule" over them, with obedience towards the Command Spells being the "absolute condition required for materialization." Due to the prospect of having a wish granted by the Holy Grail, it also serves as incentive cooperate with the Master, as well as requiring them for energy upkeep and acting as their anchor to the world. Killing them will normally go against their purpose, but the Command Spells protect the Master from those who would kill them to seek out one who would be more suitable.

The Servant system was designed to summon only the souls of "true" heroes - benevolent, honorable, and selfless protectors of humanity and justice. Due to the corruption of the Holy Grail in the third Holy Grail War, evil spirits can be summoned. These entities can still be considered to be Heroic Spirits if they were widely worshipped, respected, or feared in life.

Within the Fuyuki system, summoning full Divine Spirits is beyond its ability, and it is said the capability to reproduce phenomenon of that level would render the Holy Grail unnecessary in the first place. Only through losing his Divinity did Chiron become an existence able to be summoned, and Medusa, more of a Divine Spirit than a Heroic Spirit, became applicable only after her Divinity decreased through becoming a monster. The Einzberns were confident in their ability to circumvent their own system to bring about the god Angra Mainyu, but he was a Heroic Spirit instead. Within the Moon Cell, the recorded Divine Spirits are considered to be non-human Heroic Spirits and Servants. Though none are summoned, BB creates the Alter Egos, her own customized beings called High-Servants (ハイ・サーヴァント), by combining several of the "goddesses series" of Servants into each.

Characteristics
Servants are beings able to switch between a Spiritual Body and Material Body at will. While in spiritual form, they cannot be easily detected by enemies, due to being invisible to the naked eye and most forms of scrying, or affected by physical interference. They can travel where they please without being impeded by walls, but they also cannot carry anything in that state. Their senses are limited to spiritual sensations, so they must materialize in order to fully experience normal senses when sharing a visual link with their Master. Their upkeep cost is low when not materialized, so many Masters prefer them to stay in spirit form to lower the cost on themselves. Depending on the disposition of the Servant or a special case like Saber, such an order may be impossible. It is also hard for them to affect a Material Body in that state, so they must materialize to properly engage in combat.

While they may bleed and take damage to their organs, their true being resides in a Spiritual Core they obtain upon first materializing. Their Material Body envelopes it, and damage must be inflicted to it in order for them to be defeated. It gradually diminishes under magical energy expenditure and while sustaining bodily damage, and their expenditure will escalate under such conditions. If it is damaged through powerful magical energy, curses, or Noble Phantasms, it will be destroyed, meaning that the Servant can no longer stay materialized. The heart and head are directly connected to it, so they are a Servant's greatest weaknesses. Sustaining damage will significantly weaken it, with some Servants having it instantly destroyed and some with skills like Battle Continuation being able to at least temporarily sustain themselves.

While they have Material Bodies like humans, the composition is drastically different. They are of a much higher magnitude, so it is normally impossible for portions to be transplanted onto a human. Shirou Emiya is able to obtain Archer's arm due to them being the same person. Normally the recipient would die of shock, but being even closer than twins allows the surgery to succeed. It is still too much for him even in that case, so being connected to it slowly kills him. Sieg, a homunculus, obtains Siegfried's heart, gaining the ability to transform and a longer lifespan, yet his body is consumed by memories and Siegfried forces until no longer the same and ending transformed into a dragon.

It is possible for a Servant to possess a human, however a human's soul wouldn't be able to endure the purity, density, strength, solidity and every other aspect of a Heroic Spirit soul. Something like possessing someone's physical body and giving them a Heroic Spirit's abilities is impossible. The physical abilities, magical abilities and any being that was called a Heroic Spirit was incomparable to that of a human's. A human who had lived twenty years would have twenty years’ worth of accumulated experience, and that experience would sometimes produce magnificent strength under critical duress. But, when you possessed another person’s body, that accumulated experience became jammed and obstructed as if by white blood cells. That other person’s accumulated years of experience and your own accumulated years of experience would clash due to lack of compatibility. But there are cases where a Servant successfully possesses a human such as Ruler and Avenger.
 * Avenger creates a replication of a real person in the world of the Holy Grail and then takes over the body due to lacking a normal form.
 * Ruler is given a body by the Grail due to the previous Ruler still existing and corrupting the process of materializing her. It searches for a match with a compatible physical build, spiritual build, personality, and magical energy. The possession seals the target's former personality and spiritually installs the Heroic Spirit. After receiving clearance from the host personality, it performs a "cross-domain base anatomy backup" to be able to restore the target even if Ruler is killed. It adapts the physical and spiritual build, grants the Class Skills, grants knowledge of Heroic Spirits and the modern era, and inputs other required data. Overwriting and merging with the target's body and personality, Ruler notes having most of the target's memories. Rather than two personalities in one body, it is more that they merged into one.
 * Sieg's transformation to Siegfried is a lot closer to a possession. Sieg summons Siegfried into his flesh with the abundant Magical Energy of his Dead Count Shapeshifter: Dragon Revelation Command Spells. Sieg connection with Siegfried's heart has allowed the Heroic Spirit to descend from the Throne of Heroes, in other words Sieg is a 'shell', a being who wore the body of Saber of Black. It's precisely because he is a homunculus. Their souls are very young and therefore pure, as such they won’t be dyed by anything, and their bodies can endure any kind of transformation as well. In the first place, a homunculus was a 'molded' entity using Magic Circuits as the foundation. Since they had no accumulated experience like humans did, their souls were pure and sturdy like an infant’s. However, the homunculus was different. He had no accumulated experience. He was merely a being created in an already-matured state. Therefore, there was no rejection when he was being possessed. Though, being possessed by a Heroic Spirit for even one second is equivalent to a miracle.

Among Servants, there are also those who can cause strong effects on the bodies of their Master. Normally, the relationship between Master and Servant is the same as between owner and familiar, but there are those who possess skills that make it possible to share bodies. In those cases, the Master becomes an existence close to immortal. Of course, only for the duration of the Holy Grail War. And most importantly, it doesn’t mean that their battle power increases, so the only Servant they’d be able to fight is Assassin.

All Servants have an (属性), a status showing a clear representation of the mentality of the Servant, differing from the elemental alignment of magi. It is broken down into two parts, a combination of the principles they consider important and their personality. Principles are reflected as Chaotic (混沌／渾沌), Lawful (秩序), and Neutral (中立), and their personalities are reflected as Good (善), Evil (悪), and Neutral (中庸). Berserker Servants have also displayed Insane (狂化) as a "principle", and Mad (狂) and Reckless (暴走) as their "personalities." Differences in personality will not result in major discord, but differing principles can make Servants resolving their differences of opinions difficult. While two Servants may have the same personalities as "good", like King Arthur and Gilgamesh, their Lawful and Chaotic principles lead to differing opinions.

Others:
 * Elizabeth Bathory (Berserker) - Insane Reckless
 * Heracles - Chaotic Mad
 * Lancelot - Lawful Mad

Upkeep
Servants must maintain a certain amount of energy to remain materialized and fight, and they must have an anchor to the world, their Master or another physical being, in order to remain in the world. Their current strength is reflected by their current stores of energy, so they will lose strength as they lose energy. The Grail itself provides most of the upkeep for Servants during the duration of the Holy Grail War, so Masters, granted Magical Paths to supply energy, do not need to provide vast amounts of energy normally. More energy intensive Servants like A-rank Servants and Berserker-class Servants can still pose a great threat should they not have the ability to provide their upkeep, even draining them to death in the case of Berserkers. Those who are cognizant are able to throttle the energy they intake, keeping their output to a minimum or using only their own stores when their Masters are unable to provide their full cost.

If the Servant is without a Master, has issues with the Magical Paths, or has a Master unable to supply energy, they must supplement themselves elsewhere. As Human Spirits, they have the ability to consume the souls and minds of people and convert them into energy. Their basic abilities do not change from such nourishment, but they become tougher as their magical energy capacity increases. They can also intake semen or blood for energy depending on their method of processing it. Places like Ryuudou Temple can naturally allow them to subside longer, and draining directly from leylines is possible for some. With a full stock of energy, they can subside for a time even with the constant cost of upkeep, and they regain some energy from their own magic circuits daily. Remaining in spiritual form can decrease their upkeep, and while in material form, dematerializing weapons and armor can help cut it somewhat. Food can be converted to supply some energy, and sleeping can stop the consumption. This only helps when no action is taken due to even a single battle using upwards of twenty times as much energy as simply existing, so such methods are only stop-gaps compared to taking in souls.

Even having a full supply will not help a Servant should they lose their anchor to the world with the loss of their Master, so they must quickly seek out another contract. While normally not much of a burden, their energy noticeably drains by the second without one. Depending on the amount of energy and upkeep cost, they may only be able to stay materialized for a brief time. Saber can manage only two hours, while Caster can last two days with a full supply of energy. Those with Independent Action are able to subside without Master support for longer than others, allowing them a better chance to seek out another contract. Much like the class container, their anchor is a "passport to the current age", so losing that will mean being forced to return to the "outside." They cannot form proper contracts with other Servants, as spirits cannot link spirits to the world. Caster is able to summon Assassin, but it is an improper summoning with several complications. Rather than her being his anchor, it is the mountain gate, so he cannot leave the area. Without a Master, they are no different than regular spirits and may be affected by the Church's scripture.

It is possible to remain materialized as a normal familiar after the Holy Grail War ends, but it greatly increases the cost without active support from the Grail. Rin Tohsaka, a superior magus. has no issue in providing for Saber's upkeep, Noble Phantasm usage, and Shirou Emiya's Reality Marble at the same time during the Holy Grail War, but in-turn requires the majority of her energy and Shirou's help in keeping Saber materialized after it ends in Unlimited Blade Works. The only one easily able to maintain a Servant is Sakura Matou after becoming the Grail in Heaven's Feel, granting her a limitless supply that easily allows her to maintain Rider. Gilgamesh incarnating allows him to exist indefinitely by granting A+ Independent Action, allowing him to exist for ten years with no issues. Ruler becomes incarnated through another method, allowing him to exist for many decades.

Knowledge
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 idea that Saber may be shocked about the immediate world initially worries Shirou Emiya, but the knowledge makes such worry unnecessary. Irisviel von Einzbern first believes that Saber may find flying in a plane to be an amazing experience, but it instead seems less than expected to her. Flying in a plane is also mitigated due to her Riding skill that could potentially even grant her the ability to fly it. While not given enough information to actually drive modern vehicles, higher ranks of Riding grant the ability to manage such through intuition even if they do not actually recognize what each separate control of a vehicle will actually perform what action. Conversely, even though Ruler understands the basic principles behind the concept of a plane, she is unnerved by the idea of a mass of metal flying through the sky and only has the relief that it did not fall out of the sky after landing. With language, Rider displays the ability to speak English to his Master, Waver Velvet, and also speak Japanese to Taiga Fujimura, allowing him to easily translate between the two.

The knowledge is not all-encompassing, so concepts may have to still be explained to them. Rider is shocked at the true scope of the world compared to the area he had conquered in life, and needs to have certain areas shown to him on a map. He enjoys spending his time learning about different aspects of the world such as wars since his time, and details like the price of a stealth bomber are not immediately known to him. Saber does not understand the idea of dating until it is specifically explained. They are granted knowledge on the ritual itself, but only as much as the outside Masters are told. They do not know if its true purpose in being a method requiring all seven be sacrificed to reach the Root, only believing it to be a war for a single wish. The knowledge can change upon the nature of the war changing, allowing knowledge of the two teams of Servants and factions of the Great Holy Grail War to be given to them.

They are not granted knowledge on other Heroes through the Grail, but rather from knowledge gained within the Throne of Heroes. Witnessing traits of other Servants can allow them to deduce their true names with the knowledge even if they are from incompatible eras. Aberrations like Saber, who is not part of the Throne of Heroes due to her circumstances, are able to identify those whose legends would have been known to them in life, such as Cú Chulainn, but cannot identify the legends of later Heroic Spirits like Gilles de Rais even after being directly named.

Summoning
There are several factors that determine which Heroic Spirit the Master will summon. Performing a summoning ritual facilitates the process in which the copy of the Heroic Spirit is brought into the chosen class container. Most Masters will prepare a catalyst with which to summon their desired Heroic Spirit, but it is not absolutely necessary. Without a specific artifact, the Grail will, rather than base it on their power, chose a Servant based upon similarities to the summoner's own nature. When choosing based upon power with a catalyst, bad compatibility may make forming a bond impossible, bringing about hardships without being able to have faith in each other. When allowing for a good affinity, it may bring forth a weaker Servant, and it is possible that a single mistake could rouse bad feelings between them due to the resemblance in their personalities being so close. The Grail of Fuyuki requires seven Servants, so it will pick from anyone appropriate until it has all seven in cases where more capable magi have not summoned Servants already.

Within the Fuyuki Holy Grail War system, there is a rule making only the summoning of Western Heroic Spirits possible due to the Holy Grail being a Western, Christian, concept and that the summoning system was created in the world of Western magi. Sasaki Kojiro of the Fifth Holy Grail War is a complete aberration in many ways. Other systems like the Moon Cell Holy Grail War have no such restrictions.

It is also possible for some Servants to bring forth other Servants under limited conditions with their Noble Phantasms:
 * Alexander the Great's Ionioi Hetairoi allows for tens of thousands of Servants to be summoned within the Reality Marble. Only one can be summoned outside of it due to the corrective impulses of the world.
 * Okita Souji's Flag of Sincerity can summon a small squad of Servants to fight temporarily.
 * Shakespeare's First Folio can bring forth Servants as "characters", but they are weaker than a Caster-class Servant in function.
 * Toyotomi Hideyoshi's Sunomata Castle can summon a number of his retinue as Servants, but they can only fight outside of the fortress for a brief period due to their energy source being located inside.

Summoning ritual
While summoning ritual (儀式の召喚) are generally specific, their main goal in the Holy Grail War system is to act as a precaution to create a bond with a perfect, reliable Servant. They really only require a summoning circle, even if unskilled, and a catalyst can bypass the need of chanting a spell. Doing so can create aberrations like Gilles de Rais being placed into a normally unsuitable class or King Arthur having a bad connection with her Master that does not allow her to receive prana through normal methods. Flatt Escardos is a complete anomaly in that he is able to complete the ritual without even meaning to summon a Servant, simply by "fiddling" with the magical energy in the area. The connection to his Servant is spontaneously established, and it is unknown if it can be called a miracle, luck, or an achievement of his own latent potential. It is possible to specify in the summoning ritual that the Servant be placed under the Berserker class for those familiar with the workings of the Grail System. By adding in a specific line, Zouken Matou and the Einzbern family, as members of the Three Founding Families, were able to choose the class during the Fourth and Fifth Wars. In the Great Holy Grail War each faction has a summoning ritual according to the color that represented.

Catalyst
Catalysts (触媒) are symbols and holy relics used to attract the desired Heroic Spirit. Requiring something with a connection to the hero, it can be anything from a sword, armor, a talisman, or even their bones. While something like Rin's Pendant is an artifact holding great power on its own, it is unable to help summon a Servant. If the catalyst is one that is particularly weak, or if it is one with a connection to many different Heroic Spirits, the Heroic Spirit among the candidates that has good affinity with the Master will be chosen. Some are those that have only been connected to a single Heroic Spirit, allowing them to be brought forth regardless of affinity with the Master.

Catalysts are extremely valuable, and it can take much effort depending on the Servant the Master wishes to summon. The Mage's Association, having been collecting the esoterica of thaumaturgy for generations since ancient times, has a grand number of catalysts "numbering among the stars." Kayneth El-Melloi Archibald is able to order a relic from Macedonia, while the Einzberns have to specifically have Avalon excavated from Cornwall. Within the Fate/Apocrypha world, the spread of the Holy Grail War system means many catalysts quickly disappearing over seventy years and numerous Grail Wars. Especially those of Gilgamesh, King Arthur, and Alexander the Great are scattered and become lost over time, and Yggdmillennia specifically collects desired artifacts over decades to procure enough excellent Heroic Spirits. The Association still has enough even then to easily provide seven catalysts to their Red Faction on a short notice.

Examples of summonings include:
 * Angra Mainyu: Avesta, an old scripture and foreign folklore
 * Alexander the Great: Shard of cloth from his mantle.
 * Astolfo - Glass bottle which had a liquid stain left on it.
 * Chiron - Ancient arrow blackened by blood.
 * Cú Chulainn: Jewel on which is engraved an original rune inscribed by Cu Chulainn that had been crafted into earrings.
 * Diarmuid Ua Duibhne: Unknown, prepared by Kayneth El-Melloi Archibald in haste after his original artifact is stolen.
 * EMIYA: Rin's Pendant, a one-of-a-kind jewel kept by Emiya as a keepsake of his unknown savior over the years. Differing from normal, it is not the pendant Rin owns in the present that acts as the catalyst. Emiya is instead a case where he holds a catalyst with a connection to his summoner.
 * Frankenstein - Frankenstein's blueprints
 * Gilgamesh: The fossil of the first skin shed by the first snake after consuming the immortality elixir, and a discarded key to the Gate of Babylon.
 * Hassan-i-Sabbah: Since Hassan is the origin of the word Assassin, the class of Assassin itself is Hassan's catalyst.
 * Heracles: The Axe-sword, a slab of rock from a temple of Heracles.
 * Jack the Ripper: Jack the Ripper's knives
 * Jack the Ripper (Symbol of madness): Replica Jack the Ripper novelty knife
 * King Arthur: Avalon, the sheath of Excalibur.
 * Lancelot: Unknown, Zouken Matou mentions obtaining the "perfect relic" for Kariya Matou.
 * Medea: Literature from Colchis with ties to Medea.
 * Medusa: Mirror dug up from a temple in Eritrea, an item with ties to an old Earth goddess of Greece. It is noted to have been a weak catalyst to Medusa, so Sakura Matou's similar personality plays a role in the summoning.
 * Mordred - Shard of the Round Table
 * Ramesses II - Nefertari's necklace
 * Sasaki Kojirou : The mountain gate.
 * Siegfried: Bloodstained leaf of a Sacred Fig tree.

General catalysts include:
 * Remnant of the : Heracles,, Medea, , or other crew members
 * Shard of the Round Table - King Arthur, Lancelot,, Gawain, , , Mordred, or other members of the Round Table.
 * The, the symbol of the

Strength
Servants have six primary statistics that make up their overall strength:
 * Strength (筋力): Bodily might in terms of power.
 * Endurance (耐久): How much damage one can withstand.
 * Agility (敏捷): Quickness and speed of reaction.
 * Magical Power (魔力): How much prana can be handled.
 * Good luck (幸運): The quality of one's luck.
 * Noble Phantasm (宝具): The strength of the Noble Phantasm one owns. While the ranking will often match their strongest Noble Phantasm, it will sometimes only reflect a secondary Noble Phantasm, or display a ranking higher or lower than their available wares.

Each of the statistics and skills are translated into specific parameters, reflecting the individual ability of each Servant. They display strength and speed far beyond normal humans, showing in battle displays likened to a "dimension that is completely at odds with the physical laws of this world." Simple hand-to-hand combat between two Servants is enough to wreck a city street in a manner able to be compared to having been carpet-bombed, damaging the ground with only their footfalls, cutting metal with only the backlash caused by their weapons clashing, and tearing away iron from simply brushing against it with weapons. The usage of their Noble Phantasms can easily leave an area in complete ruin, some displaying the capability to easily wreck part of a city with minimum usage.

Both their movement speed and dexterity is enough to make them invisible to the human eye, looking like a breeze of wind when running past and only leaving the aftershocks of their attacks to be felt by onlookers. Compared to even a top-class motorcycle like Saber's V-Max able to reach over four hundred kilometers per hour, the dexterity of a Servant places them far above it both maximum acceleration and speed, and they can rival a jet fighter in speed with proper footwork. It may be still advantageous to use a motorized vehicle in a pursuit due to it only relying on its fuel rather than using their own energy up while running on foot. The speed of bullets travelling faster than the speed of sound poses no threat, unable to surpass the speed with which they wield their weapons, and those with greater dexterity can easily deflect them with their weapons. Not bound by normal logic, they are able to move up the sides of buildings simply by kicking off the sides.

Even the smallest of Servants will have little issue in carrying a person, and Rider, causally copying something out of a comic, is able to lift a vehicle from a construction site to slam down on to her opponents. For a human trying to apply pressure to a Servant even the size of a child, it feels like trying to bend a steel beam. Punches with all of their strength will not even budge them a millimeter, and even Souichirou Kuzuki, whose punch is potent enough crush a human's skull, can only slightly move Archer's head from the impact. Stabbing them with a knife does nothing but bring about a "prickling irritation" that does not hurt at all. Even those who are physically weak compared to others like Gilles de Rais and Medea display feats like grip strength enough to easily crush a human skull and severing an arm with a ritualistic dagger unable to normally even be considered lethal to a regular human.

Masters who have made contracts with Servants have the ability to read out the status of a Servant with powers of clairvoyance. It is a unique ability granted by the Grail that summoned the Heroic Spirits, so it cannot be used by those without a contract. They can see through the abilities of the other Servants and compare them to those of their own, so that they can guide them as efficiently as possible in battle situations. Tokiomi Tohsaka owned a book that provides a similar ability, but it is useless to a full Master. It was passed on to Rin Tohsaka after his death, and she gives it to Shirou Emiya because he lacks a proper connection to Saber. The book itself is blank, but simply looking at a random page gives him an image in his head that allows him to look upon all known status of Servants in the War. Reading the book will give him new details any time he reads it, and Rin says that he will be able to identify Servants from intuition without using the book after he gets used to it. It is reflected in-game as the Servant status screen.

Factors
The strength of the summoned Servants depends on various factors. It is ideal if the Servant can wield their original power as a Heroic Spirit, but it is also possible that they can even surpass their original selves in the case of the attribute enhancement from Mad Enhancement of the Berserker class. It is also possible to obtain abilities from Class Skills they did not originally have in life, such as Riding modern vehicles, or have their own attributes strengthened by their classes' natural attributes.


 * Cultural Sphere (文化圏) - The Land (土地) in which the Servant is summoned and the Recognition they receive there are two factors that play a role in their strength. The closer the are to the stage of their legend, a geographical boost, and the more that they are known makes them "stronger", bringing them closer to the strength they had in their legend and providing them with more of their equipment displayed in their legend. Depending on the circumstances, it is possible it can bless them with additional Noble Phantasms. The boost from recognition alone is not that large in making a difference in power as when Rin Tohsaka is speculating on Gilgamesh's ability to overwhelm other Servants. Land plays a greater factor with Cú Chulainn, Heracles, and King Arthur being three heroes around the same level of strength when summoned in Europe. Each would be strengthened in Europe and benefit most greatly in battle in their home country, though Heracles' fame would allow him to display excellent power throughout all of western Europe. Cú Chulainn, gaining zero influence from not being known as well in Japan, does not fully display his "shining existence" on par with them while in Fuyuki, but would anywhere else in the world. He would obtain several benefits from being summoned in his homeland, Ireland, and outfight Diarmuid Ua Duibhne, who would have an advantage when both are unaffected by the cultural sphere and have other factors at play. Vlad III gains a great boost in Romania, placing him on the same level as those famed heroes, and Semiramis gains her maximum fame while in the confines of the Hanging Gardens of Babylon.
 * Magic energy of the Master - The more powerful the magical energy of the Master, the greater the Servant will be able to reach the strength they displayed in their legend. If they cannot provide proper energy or if the Servant lacks a Master for a time, their parameters lower in proportion. If it is a lack of energy, unknown factors will lower parameters and skills with some Servants, while the Master's way of life may affect others. King Arthur, serving under several different Masters, displays a number of different sets of parameters due to fluctuating levels of energy. Under Shirou Emiya, she receives no energy because his Magical Paths are obstructed and cannot display her full strength. Kiritsugu Emiya is able to supply energy to have her be stronger than under Shirou, but her luck is affected by his personality due to still not providing enough energy. Her Riding is increased one rank higher than normal for an unknown reason. Rin Tohsaka is a excellent magus able to allow her to unleash her full abilities without being affected. Two Servants who would be balanced differently under other circumstances may find the balance tipped when one has better Master support.
 * Container Parameters: Unmodified by the strengths and weaknesses of specific Heroic Spirits, the containers of the seven standard Servant classes of the Fuyuki Grail War possess known base parameters. The parameters of the containers has not been shown to affect summoned Servants, allowing for parameters higher and lower than those of the containers.

Battle
Battles between Servants can be called a process of gradually shaving off the magical energy that forms their bodies. Attacks that consume a great amount of magical energy will inflict a massive amount of damage on the opponent, but it will also weaken the attacker in the process. In order to inflict a great amount of damage with minimum expenditure of magical energy, it is necessary for them to collect intelligence regarding the enemy and assault their weakness. The greatest weapon is their Noble Phantasm, and a battle between Servants can often be called a battle between Noble Phantasms.

When describing their strength, they can be likened to a single jet fighter in pure attack power, far beyond the ability for a single person to fight. While strong, they would have to refuel many times in order to destroy a city. Though there are many modern weapons that are more powerful, their status as spiritual bodies makes them among the most powerful due to being immune to modern weapons. Their Noble Phantasms can be likened to a jet's ability to load a nuclear warhead far beyond its normal fighting power, with some Servants having extremely powerful ones. With Servants, those with an "extremely average Noble Phantasm" would have one around the level of B rank which has strength able to be represented through numbers. Broken Phantasms, Invisible Air, and Gae Bolg's thrown strike all deal pure physical damage, while Gae Bolg's piercing version carries a conceptual effect able to kill opponents of a much higher level than the wielder.

True name
The true name (真名) 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 unless they do not care like Assassin of Black, wish to have a closer connection to their Master like Caster after she reveals her identity, or under circumstances where it no longer matters like those trapped in the Sakura Labyrinth. There are Servants and Masters with extreme confidence or no filter in revealing their true names for all to hear, such as Rider exclaiming his name without regard and Illyasviel von Einzbern having supreme confidence in Berserker even with his name revealed.

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. Those killed by poison will be more susceptible to it, those shot down by arrows will be weak against them, those with weak spots will be severely disadvantaged if they are targeted, and those with traits like being weak to monster-slayers or dragon-slaying weapons can be specifically damaged in accordance. Even without such a specific countermeasures being available to one Master, releasing that information to the other Masters can allow for other countermeasures to be brought forth. Most Masters should know instantly of their own Servants' identities, but something like Secret of Pedigree can block even that, and the refusal of a Servant to disclose it can keep them from knowing. In the case of a weak Master susceptible to mind control, they may forgo telling them altogether until necessary.

Famous heroes like King Arthur and Siegfried are very likely to have their identities found out more easily than others, with simply glancing upon Excalibur being enough for any Heroic Spirit to identify King Arthur. Others need to utilize their Noble Phantasms before they reveal themselves, but it may require deductive reasoning even then. While the oldest legend, Gilgamesh is able to show off his Noble Phantasms without many being able to guess, and despite his believing that it should be obvious to others, generally discloses it himself. Someone like Archer, being a Counter Guardian from the future and displaying numerous Noble Phantasms with Unlimited Blade Works, is a complete anomaly to others, greatly confusing all who fight him with his contradictory traits that do not match any known hero. There are also those without specific weaknesses whose true names will bring no trouble if revealed like Astolfo.

Modern weaponry
As spiritual beings, servants cannot be harmed by modern weaponry. Firearms wielded as regular weapons by Servants like Francis Drake's pistols and those ascended to the rank of Noble Phantasm like through Lancelot's Knight of Honor are able to inflict damage.

Other opponents
Beings other than Servants that are able to combat Servants are few in modern times. Beings such as Arcueid Brunestud at 30% of her strength, Amaterasu, and Kingprotea would always generally win against a single Servant due to their overwhelming ability. Arcueid could potentially be overwhelmed by two Servants fighting at once even though she is around four times as strong as one, while Amaterasu and Kingprotea require the strength of several Servants to be defeated. If speaking of a Servant with an extremely average Noble Phantasm, the members of the Twenty Seven Dead Apostle Ancestors, Kouma Kishima, and Aoko Aozaki can fight directly, while Ciel and the Shiki Ryougi's third personality can keep up in a defensive fight that can still be called a fight. Ryougi's normal personality and Shiki Tohno have no chance of matching Servants, but the Mystic Eyes of Death Perception they carry are capable of affecting such beings whether incarnated or spiritual bodies. Humans utilizing ten Command Spells would also be able to damage Servants. Kirei Kotomine and Kiritsugu Emiya at the peak of their strengths during the Fourth Holy Grail War could defeat Servants, but only when the weakest, Caster and Assassin, are at their most exposed, or when they have special conditions in their favor like surprise or suitability against the opponent.

Against Dead Apostle Ancestors, both are types of beings that live in mystery, so such battles would come down to "having the means of killing the other guy somehow." Servants will generally hold a slight advantage, barring compatibility issues, and the Knight classes, Saber, Archer, and Lancer will all be able to have solid fights. While Saber's Excalibur is extremely effective against those who overwhelm by material quantity and alienness, there are those capable of surviving being hit by Excalibur-class attacks through pure endurance. At the same time, those same ones with extreme endurance would have a tough time with Lancer's Gae Bolg. ORT, to which Earth's rules don't apply, and Primate Murder, which has an advantage against primates and requires seven Counter Guardians to control, can be called in a league of their own above both Ancestors and Servants.

Classification
Heroic Spirits summoned by the Holy Grail are place into one of seven classes. The seven standard classes are Saber, Lancer, Archer, Rider, Caster, Assassin, and Berserker. According to Rin Tohsaka, one or two Servant classes are changed between each war, so other classes, such as Avenger created by the Einzberns in the Third Holy Grail War, can also be summoned. The Three Knight classes are the only Servants that will definitely be summoned according to the framework, allowing for variation in the rest of the classes. More than one version of the same class cannot be summoned, even if all the Masters were to use the variation in the summoning chant to get a Berserker-class Servant. Within the Moon Cell Holy Grail War, the main seven are standard classes, and while others are mentioned, only the Saver class appears as an aberration.
 * Saber: Servants placed within this class are agile and powerful melee warriors. It is commonly assumed to be the best class overall, with high ratings in all categories. It is one of the three Knight classes, together with Lancer and Archer and also possesses the Riding skill like the Rider class.
 * Lancer: Servants placed within this class are very agile and skilled with long-range melee weapons, such as spears, lances, etc. It is one of the three Knight classes, together with Archer and Saber.
 * Archer: Servants placed within this class are usually proficient with projectiles and can survive longer without a Master nearby, thanks to their special ability Independent Action; the strongest Archers can be difficult to control at times, in fact, due to their near-total independence from their "Masters". It is one of the three Knight classes, together with Lancer and Saber.
 * Rider: Servants placed within this class place emphasis upon speed and powerful Noble Phantasms, which often include their mounts. Their special skill is Riding, which allows them to fully utilize abilities of their mounts (which can range from simple horses to mechanical vehicles to divine or supernatural creatures.).
 * Caster: Servants placed within this class are adept in magecraft and have a special ability akin to Reality Marble, called Territory Creation, which alters or creates space around them to enhance their sorcery.
 * Assassin: Within the Fuyuki Holy Grail War, Servants placed within this class are always, as a rule, one of the 19 Hassan i Sabbah, the leaders of the clan of the Hashshashins who passed their name down. The Assassin in Fate/stay night summoned by Caster is an exception, an aberration in the system, as he was summoned by another Servant. This rule comes from how the word "assassin" itself finds its etymological roots in that clan. This rule is not present in the Moon Cell Holy Grail War and Great Holy Grail War, allowing for those known to be specialized killers to be summoned. The Assassins' special ability is Presence Concealment, which allows them to remain undetected. Offset by their stealth is their weak combat skills. Due to this, Assassins often target Masters instead of Servants.
 * Berserker: Servants placed within this class are always heroes who have gone berserk in their lifetime. This trait allows them to use the special ability Mad Enhancement, which trades their consciousness (i.e. sanity) for a large power boost. Most Masters are incapable of controlling their Servant once Mad Enhancement has been activated, which eventually results in their death.
 * Avenger: It is not one of the seven normal classes, and it has only been used once as a unique container for Angra Mainyu in the Third Holy Grail War.
 * Saver: This is an irregular class in the Holy Grail War of the Moon Cell in Fate/Extra. The only case is of the class is Saver.  Saver is a "messiah" type Servant, and was carefully selected by the Automaton from the collective records of the Holy Grail War.
 * Ruler: Servants placed in this class govern the rituals utilizing the Fuyuki Holy Grail War's Greater Grail while its reserve system is in effect, such as Joan of Arc in Fate/Apocrypha. Ruler is a special Heroic Spirit summoned by the Holy Grail itself to act as the administrator of the Holy Grail War and has the ability to use Command Spells, which are normally only usable by Masters, to command the Servants.
 * Beast: This class is a special container for the 666th Beast in Fate/Prototype.
 * Funny Vamp (ファニーヴァンプ) is the class granted to Arcueid Brunestud by the Moon Cell should she participate as a Servant. While she takes on the Berserker class instead, Funny Vamp reflects her whimsical nature and her status as a creature that drains blood, physical energy and money from men.
 * Alter Ego: This classification is for those created by BB as High-Servants made of several goddesses.
 * Launcher: Launcher, "the Heroic Spirit of the laser beam", is a special nickname thought up by Jinako Carigiri for her Servant.
 * Gilgamesh: Gilgamesh during Fate/Extra CCC is beyond being confined to a class, so he does not have one.
 * Monster (モンスター): Monster is not a Servant classification, but rather the title given to the irregular being, Shiki Ryougi, who appears within the Holy Grail War of the Moon Cell.
 * Shielder (シールダー), Servant of the Shield, is a prototype Servant class that was originally set to appear in Fate/stay night until the character, Stray Servant, was cut from development.
 * Others: The class Gunner (ガンナー) is suggested as a possibility by Archer. Lancer declares herself to be Idol (アイドル) and nicknames Gilgamesh Gorgeous (ゴージャス). Butler (バトラー) is also used in a joking manner.

Fuyuki Holy Grail War
The events of the Fuyuki Holy Grail Wars are detailed in several stories. Some details of the Third Grail War are mentioned in Fate/hollow ataraxia. The events of the Fourth Grail War are described in Fate/Zero. The events of the Fifth Grail War are detailed in Fate/stay night and Fate/hollow ataraxia.

Moon Cell Holy Grail War
The events of the Moon Cell Holy Grail War are detailed in Fate/Extra and Fate/Extra CCC.

Great Holy Grail War
The events of the Great Holy Grail War are detailed in Fate/Apocrypha. Servants for the canceled game Fate/Apocrypha project.

Tokyo Holy Grail War
The events of the Tokyo Holy Grail Wars are detailed in Fate/Prototype and Fate/Prototype: Fragments of Blue and Silver.

False Holy Grail War
The events of False Holy Grail War are detailed in Fate/strange fake. The Saber class is absent and replaced by the Player.

Fate/Grand Order
The events of a number of Holy Grail Wars are detailed in Fate/Grand Order.

Imperial Holy Grail Strange Saga
The "events" of Imperial Holy Grail Strange Saga are detailed in Koha-Ace.

Others

 * , and  are jokingly mentioned in the Fate/Prototype Drama CD as being summoned by Ayaka Sajyou to use their powers of persuasion to end the Second Holy Grail War without any casualties.
 * Armstrong (アームストロング) is a Servant mentioned by Shinji Matou to be a participant in the Moon Cell Holy Grail War, possibly referring to the American astronaut or the famous engineer.
 * Bucephalus, Mithrenes, and the soldiers of Ionioi Hetairoi are all temporary Servants summoned and sustained by the Reality Marble.
 * Dragon Rider (ドラゴンライダーで) - The development stage of Fate/Zero was to feature a Rider who rode a dragon and had a climactic battle with Saber that ended with her using Excalibur, but Nasu could not think of one who rode a minor dragon. Alexander the Great was originally to be an unspecified, abnormal-class Servant, but Gen Urobuchi wished for him to be Rider instead and ultimately replaced the idea. Caster and his Gigantic Horror were later used to fill the place of facing Excalibur.
 * and of the Shinsengumi can be summoned using Sakura Saber's Flag of Sincerity.
 * (清姫) is a Servant in the Moon Cell. It is unknown if she participates in the Moon Cell Holy Grail War, but she is mentioned by Caster as an e-mail friend. She says that Kiyohime's method of dealing with love rivals would be to "trap them in a bell and then set it on fire."
 * (ネブカドネザル2世) is mentioned as the proper owner of the Hanging Gardens of Babylon as a Noble Phantasm, compared to Semiramis who only obtained it through history having been distorted over time.
 * (始皇帝), the First Emperor of the Qin dynasty, is noted as the most celebrated figure in Chinese history. One of his Noble Phantasms has been recovered in modern times, and it is useable as a weapon even by normal magi. The Kuruoka family believes that he will be a Heroic Spirit that requires deference even from the summoner. He is never summoned due to their daughter obtaining Command Spells and her own Servant.
 * Scathach,, the , , and are potential Servants that can be summoned by the Player.
 * Sun Wukong briefly appears in Koha-Ace.
 * was to be the Rider-class Servant of Old Fate, but was replaced by Perseus for Fate/Prototype.
 * - Urobuchi considered using one of the Chinese Xian when attempting to think of the Caster-class Servant for the Fourth Holy Grail War that eventually ended up being Gilles de Rais. Nasu explained the Western-only rule of the Fuyuki system, and felt that the Xian would be too strong.
 * Numerous other Joke Servants were designed for a contest feature in the parody 4 Koma manga Fate/school life.

Servant Parameter listing
Parameters for each Servant