Magical Energy

Prana (魔力 maryoku) is the power source that allows magecraft to be used, akin to gasoline. It has various names, most people call mana what is in the atmosphere. This is mana in the Polynesian meaning of it, mainly. Ether is again something else.

The energy mentioned in the series is both mana as well as something else, an energy that magi produce in their own body. The difference between the energy that fills nature and the energy an individual produces is just that.

In the disemboweling forest, the energy of nature is under Einnashe's control and cannot be used. Hence most magecraft do not work and has to rely solely on the energy of the individual, that is, mainly small scale magecraft.

As a side-note, Blue is one who can do absurd things with that individual energy. You could say she is able to have a car run 1000 kms with one liter of gasoline.

Another one with weird limits is Ciel. If the gasoline tank of a normal person has a capacity of 40, then Ciel's is over 4000. That's miss glutton alright.

Source: Tsukihime Dokuhon PlusPeriod dictionary entry in the Talk. short story (p.194)