Magical Energy

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” was used by Blue1 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.

Yoi No Myoujou: Talk.
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An essential element for invoking magecraft. 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 Plus Period: Tsukihime Dictionary Revised
Translator's Notes
  1. ^ Blue refers to Aoko.