Referred to as the primordial animus and life itself, Magical Energy is the source that powers all forms of magecraft. Analogous to gasoline, it is an essential element for the invocation of spells. There have been many names for Magical Energy depending on the culture. It is primarily classified by two types, Mana and Od, separated only by whether it comes from the atmosphere or from within human magi. They are essentially identical in terms of quality, but the world's Mana vastly exceeds humanity's Od.
In the Holy Church it is considered taboo to use the terminology preferred by magi due to the organization’s long-standing conflict with the Mage’s Association. Members of the Church therefore refer to Magical Energy as "prayer power".
Mana (マナ, Mana?), the meaning of which is approximately the same as that of Polynesian culture, is the greater Magical Energy found in the atmosphere of the world. It is the "breath of the planet filling the world and nature," produced by the World through a network of Ley Lines (龍脈, Dragon's Meridian?) across the globe. There also exist the Divine-make leylines (神造霊脈?) of Olympus. They are a wireless network of leylines created and administrated solely by the Gods, capable of superior mana provision compared to regular leylines.
The density of Mana on the planet is dependent on the age. Within the Age of Gods, the Mana density is such that a modern human will die when exposed to it without a specialized Mystic Code to block out the Mana. The reason for that is because humanity has adapted to an environment where Magical Energy is vanishing, and their bodies can no longer withstand their original one now that they parted from the World of Magecraft.
The Mana within a given area is finite, the three kilometer cavern housing the Fuyuki Greater Grail holding one thousand units. Similar to magi needing time to regenerate their Od, the Mana of an area will take a long time to replenish after it is depleted.
Magi utilize freely the Mana in the air for the purpose of spells that exceed their personal Od, but the amount they can utilize at one time correlates to the capacity of their Magic Circuits. If there is no available Mana, they can only utilize small-scale spells with their own storage. The Forest of Einnashe directly controls its atmosphere, so magi cannot use the Mana from environment. Satsuki Yumizuka's Reality Marble Depletion Garden rapidly depletes the Mana in the area, acting as a natural enemy to magi and Elementals. Within the World of Fate/EXTRA, worldwide Mana Depletion (魔力枯渇?) brings about the end of magecraft, many magi becoming wizards.
Known Magical Energy levels
There is some inconsistency between the various visual novels that make up the Nasuverse. In Fate/Stay Night, the average amount of Od is 25 units of magical energy. However, in Tsukihime, the average amount of Od is 40 units of magical energy.
- Average matured magus: 25 units of magical energy (Fate).
- Ciel: 100 times the amount of a magus based on an average magus having 40, giving her over 4000.
- Shirou Emiya: 20~30 units of magical energy.
- Sakura Matou: Normally, she should have about the same amount as Rin, but the Worms in her body are constantly consuming her energy. When connected to the Holy Grail and Angra Mainyu, the energy inside her body is equivalent to 1,000,000,000,000 units of magical energy, already on the level of a Counter Guardian. However, her maximum output of this energy can only equal her original amount, approximately 1000 units of magical energy at a time.
- Rider’s Pegasus: 100 times the amount of a magus, so about 2500 units of magical energy.
- Saber (with Shirou as Master): 1200~1300 units of magical energy.
- Rin Tohsaka: 20 times the amount of an average matured magus, so about 500 units of magical energy. Maximum output is about 1000 units of magical energy.
- Aoko Aozaki is capable of absurd feats of Magecraft using just her Od. An approximate comparison would be of a car traveling 1,000 kilometers with only one liter of gasoline.
- Caster’s cost for a bolt of light is around three times Shirou's full capacity, and she can launch over ten at once in multiple volleys.
- Shirou Emiya’s cost for:
- Reinforcement: 2 units of magical energy.
- Tracing: 5 units of magical energy.
- In ancient Egypt, there was a practice of sewing one's eyelids together to prevent magical energy from escaping the body.
- Saber’s consumption (with Shirou as Master):
- Battle with no damage: 10 units of magical energy.
- Amount regained per day: 8 units of magical energy.
- Amount needed to maintain her body per day: 6 units of magical energy.
- Amount spent fighting in the first day: 250 units of magical energy.
Od (オド, Odo?), from the concept of Odic force, is the life-force energy found within living organisms such as humans, animals and Magical Beasts. Once depleted, the Magic Circuits that are stored in the human soul will begin to replenish it. Od is produced as long as one lives, but the amount a person can store varies from individual to individual.
The difference between Mana and Od is their abundance. Mana can be found almost anywhere and in great quantities, thus it is called the Greater Source by the magi. As Od is the energy inside humans and animals, it is much smaller in amount and is called the Lesser Source. Strictly speaking, Mana and Od are energy in its raw state, whereas magical energy is the name given to the energy once it is converted by the Magic Circuits. Mana can be taken in accordingly with the capacities of the Magic Circuits, but the actual conversion process will take time.
Regarding nature interference Magecraft mentioned before, at least for large-scale spells, activation requires the use of Mana regardless of the amount of Od that the magus has. In fact, it is common practice among the magi to start up their spells with Od and then keep them running with Mana. Only small-scale spells that do not interact with the environment directly are performed entirely with Od, an example of which would be Reinforcement.
Magical energy itself does not have any elemental attribute. However, once embedded into an object that does have said attribute (such as jewels) or that is under the influence of Nature Spirits, it will attune itself to the elements in question until the moment that it is released.
The magical energy itself is held only inside the body fundamentally and if released in the outer world, it will return to the life force and be scattered into the Greater Source. This has also been expressed as "evaporation." If someone has Magic Circuits and they are still operating, an individual's Od will be regenerated even if is totally used up. However, without Magic Circuits, Od will no longer be generated at all.
Magical power is prone to merge with the fluids (such as blood or semen) of the magus, and these fluids are good at holding in magical energy for some time even after leaving the body. Because of this, by drinking a magus' blood, one can replenish one's magical power. Magi with monetary problems have also been said to sell their bodily fluids, in which magical energy has been merged, to the Mage's Association.
Other forms of magical energy
 Tsukihime Dokuhon PlusPeriod - TSUKIHIME Dictionary: Magical Energy [Term], p.189
Magical Energy [Term]
An essential element for invoking sorcery. Also known as the primordial animus, and life itself.
It is broadly divided into two types: the greater magical energy (mana), which is the breath of the planet filling the world and nature, and the lesser magical energy (od), which is possessed by living beings (humans).
As far as quality is concerned, they are both essentially identical. The only difference is that the amount of mana in the world far, far exceeds the amount of od.
Because mana is the magical energy of "that space" which fills the atmosphere, magi can use it freely.
…Of course, the amount that can be utilized directly corresponds to the capacity of the magus – which is to say, the number of magic circuits they have.
 Tsukihime Dokuhon PlusPeriod - talk. Glossary: Magical Energy [Term], p.194
Magical Energy [Term]
The source that powered all magecraft, analogous to gasoline.
There were many names for it. For example, the magical energy in the atmosphere was called Mana. The meaning of Mana was approximately the same as that in the Polynesian culture. Also, Ether was not a form of Magical Energy as it was something else.
The Magical Energy in this story included Mana and the Magical Energy generated by magi themselves.
The difference in magnitude between the Magical Energy that permeated the natural environment and the Magical Energy generated by an individual was so great, it was foolish to compare the two.
Since the atmosphere in the Engulfing Forest was under Einnashe's control, one could not utilize the Magical Energy of the environment. As a result, most magecraft could not be activated, a magus could only activate very small-scale spells that utilize an individual's internal storage.
As an aside, this thing called "an individual's Magical Energy" as used by Blue in a foolish yet clever manner. To use a simile, it was like driving a car for 1000 km on 1 L of gas.
Also, the capacity of Ciel was ridiculously large. If a regular magus' gas tank was 40, then Ciel's was more than 4000. She truly deserved the name Miss Glutton.
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 Melty Blood Act Cadenza PS2 Manual - Dictionary: Depletion Garden [Technique name], p.057
Depletion Garden [Technique name]
Yumizuka Satsuki's Last Arc. A reality marble.
Satsuki's powers blossomed after becoming a vampire, and this is her strongest attack. As the name "depletion" suggests, the magical energy in the deployed space is rapidly dissipated. Though it is similar to Akiha's Origami, the target of Depletion Garden is the world itself. Also, the depleted magical energy does not return to the user, Satsuki, but instead merely vanishes.
It is a field effect that could be considered the natural enemy of magi, who require magical energy to attack, and elementals, who require magical energy just to exist.
On the other hand, against organisms that are cut off from the world (for instance, humans, who don't use the magical energy in the atmosphere much at all) there will not be a pronounced effect.
 Fate/EXTRA material - Encyclopedia: Mana Depletion [Circumstances], p.211
Mana Depletion [Circumstances]
Overcount 1999. In 1970, a ritual performed in a certain local city in England in 1970 set off the depletion of the Earth's magic energy filling its atmosphere.
It caused a pole shift, a crustal movement of global magnitude later to be called the Great Collapse.
Having survived through two periods of decline – the end of the Age of Gods and the beginning of the AD calendar – magecraft finally became a fairy tale of the past.
In the EXTRA world, all that remains of the old world magi are the Atlasian alchemists of Egypt.
 Fate/EXTRA material - Encyclopedia: The world of EXTRA [Circumstances], p.163-164 [T]
The world of EXTRA [Circumstances]
“The minds of people became used to being managed and regulated, and civilization stagnated. There are no great tragedies, however there are also no new discoveries. Everyone is pessimistic in this flavorless world where you can only await death. This is our “reality”.”
Fate/EXTRA is set on Earth in 2030.
The world of EXTRA differs from that of Fate/Stay Night in that it has a different time line and events starting from 1970. History took a different path.
Mana, the energy required to carry out large scale magic, has dried up, and real magic has been lost from Earth.
The magicians of old have disappeared from center stage, and the era of magic has drawn to a complete close.
From then on those who called themselves “Magus” came to represent Spiritron Hackers, a new generation of mankind.
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 Fate/complete material III: World material - Theory of Magic - Magecraft: Using Magic, p.042
Magic is activated when a magic formula is set into motion. For example, to light a fire with magic, one must contact a magic foundation engraved in the world and activate the magic formula for the phenomenon of “igniting a fire.”
To run a magic formula, one must first generate mystic energy. As previously mentioned, mystic energy is generated through the conversion of life force with magic circuits. Magic is classified into two major groups depending on whether the internal life force of the magus (Lesser Source = od) is converted into magic power, or whether the external life force of nature (Greater Source = mana) is taken in and converted into energy.
The generated mystic energy travels through the circuit, is sent to the magic foundation, and immediately activates the magic formula. In a narrow sense, the phenomenon that the magic formula starts can be called "magic".
Regardless of the Source of power, there is no difference in the activated formula. Whether one manually cranks a power generator or builds a windmill to drive the generator, the type of "power" generated will be the same (though the magnitude will differ).
•Magic powered by the Greater Source
The Greater Source is the life force of the planet, expressed as the life force of the atmosphere and other parts of nature. It is the life force that permeates the outer world.
The nature of it is the same as the Lesser Source, but the amount is orders of magnitude greater than that of the Lesser Source. However, the amount of the Greater Source that a magus can convert at one time is limited by one’s magic circuits, so no matter how much mana is available, it cannot be used without limit.
There is also a limit to the amount of energy someone can hold at once, so it is not possible to convert the Greater Source to mystic energy in advance and build up a massive reserve.
•Magic powered by the Lesser Source
The Lesser Source is the life force of the magus itself. It is something that exists in one’s inner world so there is no process needed to absorb it as with the Outer Source, and it is accordingly easy to handle. Many magi use their Lesser Source to generate mystic energy.
As one might assume from the name “life force,” overuse will have negative consequences on one’s body. Thus, it is typical for magi to gradually generate mystic energy and build it up inside the body. Mystic energy capacity differs by individual, and excellent magi can store large amounts of energy.
•Characteristics of Mystic Energy
Mystic energy is fundamentally stored only inside the body, and if released in the outer world it will return to life force and be dispersed into the Greater Source. This phenomenon is also expressed as "evaporation.” Mystic energy easily mixes with the fluids (such as blood or semen) of the magus, and these fluids are effective at holding mystic energy for a time even after leaving the body. Because of this, by drinking a magus' blood, one can replenish one's magic power. Magus with financial difficulties have been known to sell their energized bodily fluids to the Association.
 Tsukihime Dokuhon PlusPeriod - TSUKIHIME Dictionary: Magic Circuit [Term], p.188-189
Magic Circuit [Term]
The foundation for setting up Thaumaturgy. There are two types, but here it refers to the quality within a human body that makes a magus a magus.
Magic circuits are responsible for converting life force into magical energy, and for connecting to the underlying grand sorcery formula.
Basically, sorcery is a formula that causes nature interference by starting up and stabilizing a "rule already established in the world" with magical energy. Or to put it another way, the "rule" is a car, and the "magical energy" is the gasoline that makes it run.
In order to start up sorcery, three things are required:
the necessary amount of magical energy, a key (password/spell/code), and magic circuits to inject the magical energy into the "engine".
If we assume for a moment that magical energy is electricity, then magic circuits would be both the reactor that produces that electricity, as well as the pipelines for running the system.
Because vital activity is indispensable to the operation of this reactor, there is a common misconception that a magus' body = magic circuits. However, though quite rare, magic circuits that continue rotating on their own even after the practitioner's vital activity has stopped do exist.
The reason that an individual's magical energy (od) will be regenerated even if is totally used up is because the magic circuits are still operating. But on the other hand, without magic circuits, magical energy (od) will no longer be generated at all.
They are spread throughout the entire body as pseudo-nerves, and can basically be divided into cores, and pipes that connect these cores together. The pipes are similar to the synapses within the brain, constantly breaking off and reconnecting, but the cores never change.
Strictly speaking, these cores are the actual magic circuits.
They are considered to be a sort of internal organ, that will never increase or decrease in number. Of course, extracting and transplanting them is technically possible, but just like implanting an extra organ into a human body it should go without saying what will happen if you try it.
Magic circuits, once lost, will never return.
As for what magi actually use these magic circuits for, well, that's covered in a different story.
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