Magic Circuit

thumb|300px|Magic Circuits.
Fate/stay night - Day 1: One day - Training (Magic Circuit) are a pseudo-nervous system that spreads itself through the human body and what qualifies a person to be a magus. 
The Magic Circuits have two basic functions; one is to convert into magical energy and another is to allow their owner to access . 
The Magic Circuits are also paths that connect the material world to the astral plane. To perform Mysteries, a magus sends a command and magical energy to a Thaumaturgical Foundation through his Magic Circuits and activates one of the included in the Thaumaturgical Foundation as if someone switched a computer on and sends it commands to run a computer program.
==Mechanisms==
Circuits.jpg|Various states of Shirou's Magic Circuits.
The Summoning ritual's effects on Rin's body.png|Rin Tohsaka's Magic Circuits being affected by the Servant Summoning Circle and the mana she absorbed to start the summoning.
Shirou's Magic Circuit in his left hand.jpg|Shirou's Magic Circuits in his left hand.
Shirou's Magical Circuits glowing (Ufotable).gif|Shirou's Magic Circuits glowing in the Ufotable anime.
Archer's Magic Circuit about to invade Shirou's body.gif|EMIYA's Magic Circuits invading Shirou's body.
Shirou about to vomit due to Archer's Magic Circuits invading his body.gif|Shirou about to vomit due to the Magic Circuits invading his body. 
Magic Circuits reside within the magus’ soul,Fate/stay night - Heaven's Feel (route) - True End: Return to the Spring and what is found on the body is just a physical expression of them that stretches itself throughout the body in a fashion similar to the nervous system. They are composed of core components, which are the actual Magic Circuits so to say, and bypasses that connect those components to the brain. Magic Circuits do not change, and once damaged, they cannot be repaired. 
Because organic activity is necessary for the operation of Magic Circuits, it is a common mistake to think that they are literally a part of the magus body. There are rare occasions in which the Magic Circuits continue working even after the practitioner’s body has ceased all vital functions. In these cases, destruction of the brain is necessary to stop the Magic Circuits. Their and are ranked through letters like magecraft, and their , that describes the overall ability, often varies between magi.
Like any other organ, the number of Magic Circuits that one possesses is determined at birth and cannot decrease or increase naturally, meaning that those from older lineages will be more powerful, but it is possible to change that number artificially through a number of methods. One of those methods is through the establishment of a mystic pass between two Magi from which the Magic Circuits can transferred. As the Magic Circuits are located in the soul, a fusion of body and mind is required during the transplant. However, the process carries the same risks and complications as an organ transplant. Furthermore, as the Magic Circuits become unstable if tampered with while in use, there is a possibility of mutual destruction if a contract similar to that between a Magus and his familiar has not been established beforehand.
For that and other reasons, lineages of magi do not seek to tamper with the Magic Circuits of their members while they are alive, but rather try to produce descendants with the greatest "extra" number of Magic Circuits possible. Note that number is not everything, and quality and precision of the Magic Circuits are also an important factor that differs from lineage to lineage. The Aozaki bloodline is known for producing magi with a low quantity of Magic Circuits, but the great quality of their Magic Circuits is more than enough to compensate for that. Meanwhile, the Barthomeloi possess a powerful brand of Magic Circuits known as .
A normal person rarely acquires Magic Circuits but in these cases they are considered as sudden mutations. While Kirei Kotomine was born with sudden Magic Circuits not of his lineage, he is not of this type. Kirei's Magic Circuits were a gift from the divine sacrament, rewarding his father, Risei Kotomine, for years of pious worship. Kirei was born with "the right to recreate the miracles in the divine sacrament". This "right", in other words, was the Magic Circuits. It is also possible to be born with atrophied Magic Circuits such as in the case of Shinji Matou.
;Known numbers of Magic Circuits by characters:
*Average Magus: 20Character material - Tohko Aozaki: Introduction, p.24
*Aoko Aozaki: Implied to have no more than Touko does.Character material - Aoko Aozaki: Explanation, p.9
*Arlette Escardos: 60The Adventures of Lord El-Melloi II Volume 8: Fem's Casa (Lower) - Chapter 1
*Cornelius Alba: Implied to have more than both Touko and Araya do.
*Ithillid Morganfarce: 90
*Luviagelita Edelfelt: 100 in total.
*Rin Tohsaka: 40 main Magic Circuits and sets of 30 sub Magic Circuits. Maximum output is of 1000 units of magical energy.Fate/stay night - Heaven's Feel route - Day 16: FINAL - Gem Sword Zelretch
*Sakura Matou: About the same numberFate/stay night - Heaven's Feel route - Day 11: beautiful (II) - Tohsaka Rin (III) and maximum output as Rin's.
*Shirou Emiya: 27
*Souren Araya: 30
*Touko Aozaki: 20. She is the first in the history of her family with so many Magic Circuits. Her parents have none whatsoever.
*Waver Velvet: 9
Still, the Magic Circuits are ultimately something unnatural for the human body and their activity will cause pain and numbness to the magus. Their very presence in the human body is something uncommon and an ordinary person will have little to none. Also, the use of Magic Circuits increases the Magus bodily temperature, which is what allowed Kiritsugu Emiya to discover enemy Masters on the battlefield through the employment of a thermal sensor during the Fourth Grail War.Fate/Zero Volume 1: The Untold Story of the Fourth Holy Grail War - Act 3 Part 1 -162:26:39
Magic Circuits are "opened" when magical energy is run through them for the first time. Based on their experience at that time, a magus makes their own mental trigger to activate their Magic Circuits at will from then on. For this reason, the triggers are different from each other and in an extreme case, self-injury can be regarded as a switch. An unexpectedly large number of magi have sexual excitement as their triggers and moreover many of them rely on drugs. Lord El-Melloi II Case Files Volume 1: case. Adra Castle Separation - Chapter 4 Part 1 (translated by TwilightsCall)
;Known mental triggers by characters:
*Flueger: to walk through a desert feeling thirsty.
*Gray: a spark that becomes a ghostly flame, swirling, spinning, roaring in her chest.Lord El-Melloi II Case Files Volume 3: case. Twin Towers of Iselma (Lower) - Chapter 2 Part 3
*Luviagelita Edelfelt: to imagine her heart as a jewel shattering. Lord El-Melloi II Case Files Volume 1: case. Adra Castle Separation - Chapter 3 Part 2 (translated by TwilightsCall) 
*Rin Tohsaka: to stab her heart with a knife.
*Shirou Emiya: to fire the hammer of a gun.
*Sigma: himself, falling asleep.Fate/strange Fake Volume 7 - Interlude: Audition
*Kanata Akagi: Waves flowing in and out.Fate/type Redline Chapter 19.3
 
Shirou failing at reinforcing a rock.gif|Shirou trying to use Reinforcement only to fail due to his repeated use of creating Magic Circuits.
Shirou in pain due to him sending his Magic Circuits to a state of shock (Ufotable).gif|Shirou feeling numb in his shoulder and back due to his Magic Circuits going in a state of shock.
Archer activating the rest of Shirou's Magic Circuits.gif|EMIYA activating Shirou's dormant Magic Circuits.
Prior to the Fifth Holy Grail War, Shirou believed that he had to "make" a new Magic Circuit every time he wanted to perform magecraft. In each attempt to do so, he temporarily (and inadvertently) converted parts of his nerves into makeshift Magic Circuits. A very dangerous procedure, as failure would result in his body breaking down from the inside out and even with success the resulting pain would be comparable to inserting a hot iron rod into the spine. Furthermore, when his natural born Magic Circuits were finally opened, his nervous system went haywire due the sudden intake of magical energy. At first, neither of his teachers of magecraft (Kiritsugu and Rin Tohsaka) noticed that habit of his.
A lesser known function of Magic Circuits is that they can be used to record and store information, in a manner not too dissimilar from computers or smartphones,Clock Tower 2015 - 04 - The Record of Lainur Gusion Lord El-Melloi II Case Files Volume 4: case. Mystic Eyes collection train (Upper) - Chapter 4 Part 2 like replaying scenes seen in one's head.Lord El-Melloi II Case Files Volume 2: case. Twin Towers of Iselma (Upper) - Prologue Any magus that is at least somewhat capable use them as a calculator in addition to their brains when solving problems.Lord El-Melloi II Case Files Volume 9: case. Grand Roll (Middle) - Prologue They can also be used as a precise internal clock to keep track of time.Lord El-Melloi II Case Files Volume 10: case. Grand Roll (Lower) - Chapter 5 Part 3 Some magi use their Magic Circuits to compute translations.The Adventures of Lord El-Melloi II Volume 2: The Devil of the Wandering Sea (Upper) - Chapter 2 Part 1 Whether it's calculation or communication, Magic Circuits can do as much processing as a mobile terminal can do.
As demonstrated by Fiore Forvedge Yggdmillennia and Kayneth El-Melloi Archibald, it is possible for Magic Circuits to negatively interfere with the user's body, either through birth or through outside interference.
In Fiore's case, she was born with defective Magic Circuits in both of her legs, and this deficiency not only profoundly affects her magecraft, it also caused both limbs to stop working, causing her excruciating pain at times. The only possible way of healing would be through removing the Magic Circuits in her legs. In other words, it would mean giving up the path of a magus.Fate/Apocrypha Volume 1: Apocrypha: Great Holy Grail War - Chapter 3
In Kayneth's situation, he fell victim to Kiritsugu Emiya's Origin Bullet which destroyed his Magic Circuits, rendering him unable to practice magecraft. The fact that he survived in his debilitating state was due to his quick attention by Sola-Ui Nuada-Re Sophia-Ri, who restored his internal organs, but the muscles and nerves were irreparably damaged. At first, he was completely paralyzed, with no hope of walking again. Fate/Zero Volume 2: The Mad Feast of Kings - Act 8 Part 1 -122:18:42 It took a large sum of money and a Puppet maker to get only his hands in working order, and that only allowed him to move within the confines of a wheelchair.Fate/Zero Volume 3: The Scattered Ones - Act 11 Part 2 -82:09:51
Reines El-Melloi Archisorte has a condition where her Mystic Eyes quickly overheat when they come into contact with magical energy, to the point where the burning sensation is compared to an allergic reaction, thanks to the immaturity of her brain and Magic Circuits. The development of her brain and Magic Circuits did not catch up with that of her Mystic Eyes, causing them to overreact in response to their use. However, as a side effect, it is due to this overreaction that her accuracy in magecraft has become prominent.Lord El-Melloi II Case Files Volume 3: case. Twin Towers of Iselma (Lower) - Chapter 2 Part 3
Luvia & Lord El-Melloi II.jpg|Lord El-Melloi II connecting to Luviagelita Edelfelt's Magic Circuits.
Ritsuka connecting to Ishtar's Magic Circuits.gif|Ritsuka Fujimaru connecting himself to Ishtar's Magic Circuits.
It is possible for magi to connect to the Magic Circuits of other magi, however, this is considered insanity. By connecting to someone's Magic Circuits, the receiver of the connection had absolute control. For a magus of mediocre ability, the receiver of the connection would easily be able to manipulate, or even burn, the Magic Circuits of the connected magus. Considering how Magic Circuits are linked to the body's nerves, it was similar to a magus placing his living heart into the hands of the magus receiving the connection. With the connection, one of the effects of the connection was that a magus could flow their own magical energy into the recipient of the connection. Lord El-Melloi II Case Files Volume 1: case. Adra Castle Separation - Chapter 4 Part 7
==Equivalents==
*Magical Energy Reactor
Dragon.jpg|Artoria Pendragon's Magic Core, the Dragon of Albion.
SaberCircuit.jpg|Artoria Pendragon's Magic Core.
Differing from the Magic Circuits of regular humans, Artoria Pendragon and Siegfried when he was alive have a granted by their Dragon blood. Its capacity is far greater than any human can achieve. While a magus' body can be considered a machine which creates magical energy, Artoria's Magic Core acts as a factory which creates magical energy.
Gray also gets a Dragon Magic Core after Artoria is summoned as Saber in the Fifth Holy Grail War, with the summoning affecting Gray's body due to her nature, and turning her more into a perfect clone of Artoria.Lord El-Melloi II's Case Files Volume 10: case. Grand Roll (Lower) - Chapter 5 Part 2
For Divine Patterns, see Fairy.
===Regression to the Age of Gods===
Beings like Lugh Beowulf, Arcueid Brunestud (Remake) and Tiamat have as their own style of Magic Circuits. It represents the extent at which they are capable of producing Mysteries that existed on Earth before Magic. They are ranked with quantifiable letters like Magic Circuits.
Their Quality ranking represents "how distant from what humans are capable of" when reproducing their pure Mysteries. Their Quantity ranking represents power, the higher the quantity, the greater the degree of influence over the surrounding environment. The C-rank Quantity allows for the display of power over a village at most. Their Composition represents the era of the "Mystery", such as Runes, Kabbalah, and Black Magic do so in magecraft. While similar in concept, things like Alice Kuonji's Ploys are not from the Age of Gods and cannot be assigned a number in Regression to the Age of Gods.
==References==
it:Circuito magico
vi:Mạch Ma Thuật
Category:Magecraft terminology