Souls (魂, tamashii?) are a record, the memory the world has; it is the second element. An existence independent from the body, it doesn't belong to the material world like the body, but to a concept above it, on an astral plane. It is the source of energy of a spiritual body.
Memories and Magic Circuits aren't stored in the body, but in the soul.
While magi believe them to exist and act as a necessary element for usage of magecraft, it is said only one magus as ever truly understood the soul. The have always been hard to handle even since ancient times, and even the ability to harvest them would prove meaningless due to the energy being unable to be converted into anything else. They are simply viewed as "things to be investigated" and "things to be moved into containers" rather than having any applicable use in such a state. On the other hand for beings with spiritual bodies like wraiths and Servants and beings like unicorns, they act as nourishment. 
Heroic Spirits are considered souls of the greatest purity among humans, said to be vast and overwhelming compared to living humans, that can fill the Greater Grail with only seven. Gilgamesh in particular is noted to be worth hundreds of thousands of human souls, and he alone is enough to fill the rest of a Lesser Grail when only the souls of four Servants have been consumed compared to the required seven.
The Hundred-Faced Hassan was born with a compartmentalized soul despite having a singular physical body, resulting in them manifesting as multiple personalities in life much like multiple personality disorder. As each is a different soul with a unique personality, they are able to manifest in different shapes once they are no longer bound by his living body as a Heroic Spirit. 
The soul is an existence that is eternal and indestructible in the material realm, but it cannot remain in this world without the body. Anchored inside the body, it can reshape itself within the body, but as it is fixated in the body, its fate is linked to the death of the body, and lasts only as long as the lifespan of the body.
When the body dies, the soul disperses and gradually fades away back to the Root to be recycled. This also applies to Servants, and magi need to feed them with prana to maintain them - something that shouldn't be doable normally on one's own, unless backed up by the Great Grail. This applies again when the Servant is killed, but the Holy Grail is here to store them temporarily to power the Great Grail.
As it is a record, as long as the soul is undamaged, even if the body loses its genetic information, it is able to restore itself as it was. However, the soul still naturally decays. In Zouken Matou's case, his very soul was still rotting: the body was restored, but it was restored as aged, and it started decaying again immediately. Similarly, vampirization - that is, making the flesh undead - is a way to prolong the soul after the death of the body; yet, the soul still decays. Vampires need to drink the blood of humans to maintain their body, and thus, their soul.
Generally, the soul is only "what fixes the subject", a vessel. The soul is an element required to perform magecraft, but handling it is very difficult: to magi, it is an unchangeable, unreachable energy, therefore, meaningless to them.
The core that binds the soul is the head - the brain. It is said that there are three parts required for a lifeform: the soul, the brain, and the body. The brain keeps the soul anchored to the body. The soul can reshape itself with the brain and the body. Usually, it is said that destroying either two out of these three is required to completely kill someone. In the case of a vampire, it seems the vampirization, which transforms the soul, can bypass the necessity of the brain to hold the soul: after a while, vampires can regenerate their body, and thus, their brain, to maintain the soul.
Michael Roa Valdamjong is probably the only one who ever succeeded in turning the unchangeable soul to a changeable information; it is how he acquired his nickname of Infinite Reincarnator (転生無限者, Tensei Mugensha?). However, revival of the soul is difficult, and what really transmigrates is his tenacity more than the actual Roa.
As he can't actually transfer the whole 100% of his abilities, he reproduces them, and always ends up inferior to the previous incarnation.
Souls are noted to have color, at least in the case of Gilgamesh and his soul that glows golden.
- ↑ Fate/stay night - Prologue day 3
 Tsukihime Dokuhon PlusPeriod - TSUKIHIME Dictionary: Seventh Holy Scripture [Weapon name], p.184 English | Japanese
Seventh Holy Scripture [Weapon name]
The conceptual armament that Ciel is authorized to carry. An iron hammer created by the Church in order to renounce the heretical doctrine of transmigration.
It was created by felling a miraculous beast said to consume souls, then using its horn as a key. The surface of the horn is inscribed with tightly-packed complaints about how "transmigration is really lame".
Since it's been almost a thousand years since it was first created, it even has an elemental living within it.
It was sanctified over the course of many years, but eventually fell into Ciel's hands.
"A horn!? That's not practical at all. The higher-ups are totally out of touch!"
Unable to hold herself back, she set about improving it, and because of that the Scripture's elemental ended up having the essence of its personality warped.
Before Ciel remodeled it, it was only effective against spiritual entities. Now, however, it has been transformed into a lump of iron that can pound a vampire to death with its physical attack power alone. It has a gross weight of 60 kilograms, and a maximum weight of twice that with optional attachments. It's a… Gatling scripture!?
 Fate/side material - Encyclopedia: Dress of Heaven [Armament], p.067 English | Japanese
Dress of Heaven [Armament]
A magical artifact passed down by the Einzberns.
As the heart that governs the Great Holy Grail, it is imbued with sorcery that can materialize the soul for just a few seconds.
Though the dress is pure white, it is actually made of gold. It is inlaid with seven "rings" said to control creation, and the souls of others.
The seven holes in the dress are the seven transformed rings, and they are designed to light up one by one every time a Servant's soul is harvested.
Since any human who touches the dress will be turned to gold, its management must be handled by elementals, demi-humans, or homunculi.
 Tsukihime Dokuhon PlusPeriod - TSUKIHIME Dictionary: Serpent [Colloquial term], p.188 English | Japanese
Serpent [Colloquial term]
Roa's nickname. The Dead Apostles gave it to him, in reference to the way he lives on through reincarnation. Given that he dabbled in alchemy, it's quite fitting.
Of course, when you hear alchemy the first thing you think of is Sion, but Sion is an Atlas alchemist, which is something totally different from those alchemists that devoted themselves to Western sorcery. It seems that the Atlas alchemists don't think much of Roa for that very reason, even though they both subscribe to the common idea that "everything flows". Also, contrary to what you may expect, Sion too is possessed of this same elitism, and looks down on Roa on principle.
…Huh? Then are Sion and Ciel actually on bad terms…?
 Fate/side material - Encyclopedia: Servant [Magecraft], p.061 English | Japanese
The Heroic Spirits summoned by the Holy Grail. They fell under the "Familiar" classification.
Seven Classes (only) were designated in advance. They were souls of the greatest purity called forth by using relics tied to the specific Heroic Spirits.
Originally they were not existences that could be controlled by mere humans, but they were forced to cooperate with the Masters due to the Command Spells. These Command Spells represented Masters' right to rule. For Servants, obedience towards the Command Spells were "the absolute condition required for materialization".
Servants could revert to Spiritual Form at any time. While in Spiritual Form, they could pass through inorganic matters that lack mana.
During Lancer's surprise drop attack from the ceilings at the Emiya residence, he phased through the roof and entered the living room. He then materialized after clearing the ceiling.
While in Spiritual Form, Servants were not affected by physical interference. However, their abilities to affect the material world decreased. As a result, it was considered advantageous to materialize during combat.
- ↑ Fate/Apocrypha - volume 2
- ↑ Heaven's Feel route day 12 - Nightmare, awakening
- ↑ Heaven's Feel route day 13 - Misery
 Fate/Zero material - Encyclopedia: Hundred-Faced Hassan [Servant], p.103 English | Japanese
Hundred-Faced Hassan [Servant]
The Assassin Heroic Spirit who participated in the Fourth Holy Grail War. One of the "Old Man of the Mountain" amongst the generations of Hassan-i Sabbah.
He was an exception in Hassans, as he did not undergo the body modification called "Zabaniya". Instead, he took advantage of his affliction of Multiple Personality Disorder and acted as an assassin without a true identity.
When summoned as a spiritual entity and emerged as a Servant, segments of his compartmentalized soul each materialized as an individual. However, due to the potential of the spirit being only that of one person, the abilities of the Assassins produced by the division were extremely low, reaching the nadir of the capabilities of Servants.
In addition, each personality has his strengths and weaknesses. Among them, there are impatient glory-hounds who ignore orders like fools, and individuals who are terrible at ambushes despite being assassins. However, if one can comprehend their characteristics and apply their skills in the right situations, the Hundred-Faced Hassan can be a very dangerous Servant. Unfortunately, because his Master had no intention of winning the war, he was damned to the fate of a voyeur.
The Hundred-Faced Hassan was summoned by Kotomine Kirei when he was still a lackey of Tokiomi Tohsaka, thus he was truly a servant of a servant. Even so, he still harboured a wish that he hoped the Grail could grant (by the way, it was "to have a perfect and unified personality"). He even plotted to hijack the Holy Grail before Kirei and Tokiomi, had the war have gone in their favour. However, in the end he did not even have a chance to show his rebellious side before becoming the first Servant eliminated from the war.
- ↑ Fate/Zero - volume 2
 Tsukihime Dokuhon PlusPeriod - TSUKIHIME Dictionary: Vampire [Term], p.178 English | Japanese
A general term for those that suck human blood. Refers specifically to the Dead Apostles, or those that have become bloodsuckers because of them.
The vampires in Tsukihime extract human blood to maintain their own flesh. If, during this process, the vampire injects their own blood into their human prey, that human will be unable to peacefully pass away. For a normal person, death will still find them before long regardless. However, on rare occasions, if the victim has high physical potential and the capacity of their soul is excellent, they will remain in the world of the living.
Afterward, their corpse is interred, and left alone for several years. During this time their brain melts, their soul is liberated from the cage of the body, and finally they arise as a kind of living dead called a "ghoul".
As a ghoul, they feed on the corpses sleeping in the graves around them to supplement their own missing flesh, restoring their physical body little by little. After many years of this, they will eventually regain their brain and intelligence. At this stage, they can finally be called a "vampire".
However, although this new vampire can move by their own will, they cannot escape from the rule of their sire's blood. Finally, after spending decades acclimating to life in the darkness, the vampire will begin attacking humans to create servants of their very own, while remaining subservient to the vampire that made them.
In order to obstruct this infinite cycle, the Church created the Burial Agency, Inquisitors that exist to slay Dead Apostles. The Burial Agency's goal is the utter eradication of all vampires, and the sealing of the 27 Ancestors that made them.
 Fate/side material - Encyclopedia: Gold-glitter [Others], p.059 English | Japanese
The name Rin called Gilgamesh when she saw him.
Gil was called "golden" not only because of his armour when he was fully armed, but also the fact that his soul glowed golden.
The wealthiest character in this story, our Gil.
His compatibility with large-spender Rin was the greatest, but that was the secret just between you and me.
|Bounded Field • Conceptual Weapon • Gradation Air • Magic • (Second Magic • Third Magic • Fifth Magic) • Magical Spells • Marble Phantasm • Mystic Code • Mystic Eyes • Mystic Eyes of Death Perception • Psychic • Reality Marble|
|Demons • Divine Spirit • Dragon • Familiar (Dragon Tooth Warriors) • Homunculus • Humans • Magician • Magus • Phantasmal Species • Spirits • Vampire|
|Holy Grail War|
|Command Spells • Great Grail • Heroic Spirit • Holy Grail • Master • Noble Phantasm • Parameter Rules • Servant • Servant classes • Skill|
|Church • Demon Hunter Organization • Mage's Association • The Twenty-seven Dead Apostle Ancestors|
|Akasha • Chants and Incantations • Elements • World • Magic Circuit • Prana • Soul • Magic Crest|