Essence

Spirit Energy, alternatively translated as mana, is a kind of "life force" possessed by humans, elves, and other living things in the Monster Girl Encyclopedia world. It forms one half of a metaphysical yin-yang relationship with the opposite demonic energy of the monsters. Very similar to the Eastern concept of qi, spirit energy is lost by vigorous activity and magical spellcasting, while it is replenished by food, rest, and living in a healthy environment. Although monsters do not innately possess spirit energy, they all greatly hunger for it, and for some monsters it represents most of their diet. Since male semen contains highly concentrated spirit energy, this makes it the monsters' most delicious food.

General features
A mystical, metaphysical substance, spirit energy is generated by all living things except monsters and elementals. Small amounts are contained in organic foods like meat and plants, but it is intelligent life which produces it in the greatest abundance. Angels and elves both have more than humans, which provides them a limited degree of magical protection from monsterization. When spirit energy is expended, males replenish it naturally from within themselves. Females do the same but less quickly; they can also replenish their reserves by absorbing the the energy which is emitted passively by grass, plants, and other living things in the environment. While useful in human lands, this becomes a ruinous liability in demon realms, where absorbing demonic energy from the surroundings causes monsterization via mana corruption.

Monsterization of women occurs when so much demonic energy is poured into the victim that her internal spirit energy production ability is extinguished, turning her into a creature of only demonic energy. This is impossible in men except for those of very particular psychologies; instead, for males demonic energy in their system spurs spirit energy production into overdrive, like an immune response. Persistent exposure turns a man into an incubus, a creature of both demonic and spirit energy.

Although a few humans can command elemental magic, the vast majority of human mages use spirit energy magic. It is not clear whether magical skill is something that anyone can learn, or whether it's genetic; but by either nature or nurture, some people are better at it than others. Demonic magic looks very similar to spirit magic - to the extent that many people in the Monster Girl Encyclopedia world make no distinction - but the underlying energies are entirely different. Overuse of spirit magic - just like overuse of physical skills - causes exhaustion as spirit energy leaves the body; some monstergirls, particularly akanames and beelzebubs, love licking mens' bodies precisely to get at the spirit contained in sweat. But all monsters prefer semen best of all, as the white stuff contains much more spirit energy than any other source.

When they have a husband, monstergirls can become so enamoured with the taste of his spirit energy that they become addicted to it. Married monstergirls also become extremely good at detecting their husband's spirit scent, and can essentially track him down wherever he is. For unattached monstergirls who eat spirit energy, like succubi, a dietary supplement is brewed by golems wherein a limited amount of semen that the automata milk out of their victims can supply many monsters with nutritional, if foul-tasting, energy.

The Demonic Energy of Monsters
Demonic energy is the vital energy that all monsters have inside of their bodies. Monsters always have a race specific demonic energy along with Succubus' demonic energy that pours into them from the Demon Lord. Compared to humans, many of them have high magic power.

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The Source of Demonic Energy
Since demonic energy is mainly produced by absorbing “male human spirit energy” and converting it into demonic energy inside of their body, it is purported that the more an individual has sex with men, the higher the magical energy she will possess. Due to this magical energy, the spells they use are often vastly more powerful than similar spells used by ordinary humans. Some of them even have magical energy powerful enough to level a small town. However, of course, being monsters, they wouldn't use their magic power for something like that. Instead, it is mainly used for spells to seduce men, or enhance sex with men. Succubus' demonic energy is an energy that is especially well suited for charm and aphrodisiac spells, etc. In the present, since all monsters have at least a bit of succubus' demonic energy, the charm spells which were only used by some monsters such as succubus, etc. are now regarded as the chief fundamental spells that monsters use. Furthermore, not all monsters can use high level spells. Even if all monsters have magical energy inside their bodies, they may not know how to use that energy freely, or they may not have the intelligence necessary to use it. Some races are not good at handling magical energy, and some can't handle it at all. For such reasons, there are many monsters that can't use spells at all.

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The Various Roles of Demonic Energy
Aside from spell casting, small amounts of demonic energy are naturally continually released from the monsters' bodies. Monsters are always in a state where they're draped in demonic energy. This demonic energy that is released is used by them unconsciously for various purposes. When they have sex with a man, the energy serves to protect the man's body. No matter how roughly and how long they have sex, the man's body never enters an abnormal state worse than fatigue, and he can never die due to sex. It also ensures that the man won't be harmed by the monster's horns, scales, etc. If the man touches the tip of a pointed horn or scale, the demonic energy covering the horn or scale gently pushes him back with a feeling like the touch of soft skin.

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Demonic Energy of the Succubi
Monsters are beings that are always under the influence of the demon lord, so all monsters currently have at least a little of the current demon lord's succubus' demonic energy stored inside their body. The demonic energy that they release outside of their body also contains some of the succubus' demonic energy. It is the most appropriate type of magical energy to be used for casting charm, and aphrodisiac spells.

Currently the special traits of all the monsters were strongly influenced by this demonic energy. The succubus' demonic energy is one of the important elements that gives shape to the current world of monsters. The succubus demonic energy is extremely powerful, and if a human is infused with it, the spirit energy that the human originally had spills out as though having been expelled. As a result, in the case of men, they'll spit out a lot more spirit energy for the monster, and their transformation into an incubus will be greatly hastened. In the case of women, the inside of their body will become filled with the succubus' demonic energy, and they'll change into a monster from there. Land that is always full of this demonic energy and firmly under the demon lord's power is called the demon realm (p. 228). Since the monsters of this land have vast amounts of this demonic energy, they are far more powerful and lustful in comparison to the monsters of other lands.

''Translation Note: Basically the same word is used for human energy and monster energy (except when monster's refer to human energy as spirit energy) and so in the translations the term "demonic energy" is used when the context refers to the special energy of monsters. "Monster's magical energy" would also be pretty accurate but is longer and so not used here.''