Magicule

Magicules (魔素) or Magical Energy, or Magic Essence, is another type, of energy, or a special type of energetic material, apart from the regular Physical Energy that permeates throughout the Tensei Shitara Slime Datta Ken World. It is described to be the building block of all magical/demonic life.

Properties
Magicules, are formed by Spiritrons. Although being a special kind of energy by nature, magicules are still able to have causal effects on regular physical matter and physical phenomena as well.

Many spiritual lifeforms entirely consist of Magicules, and thus physical attacks do not have any "proper" effect on them. One would need Magic, Skills, Battlewill, or Weapons that can affect spiritual matter to deal proper damage. An example of this would be Eren attacking Ifrit's salamanders with her Icicle Lance.

The natural laws that govern magicules concerning physics aren't known. However, there are noticeable deviations from the usual rules that govern physics, like the laws of Thermodynamics, or laws of Energy Conservation — to the extent of being outright broken.

Effects
To any lifeforms that are not Monsters or Humans that turned themselves into Majin (Humans usually possess little to no Magicules in their bodies), Magicules are toxic, and might even cause them to die if the Magicule concentration is high enough.

However, there are exceptions like some animals, plants, or Humans that might survive the toxic effects of the demonic matter and instead mutate to become Monsters themselves. Creatures whose bodies tend to be more based on Magicules than physical matter the higher their Rank also have higher resistance to Magicules.

Other exceptions; are those who build up their innate resistance against Magicules or evolved into higher levels like Enlightened and Saints. Other than that, even Elementals are susceptible to Magicules. Since coming into contact with Magicules might corrupt them and turn them into monsters. Even the Elemental Queen is no exception to that.

It should be noted that even Monsters themselves have a tolerance limit and can be harmed by an overwhelming amount of magicules. Even when sealed in the Sealed Cave, Veldora's aura prevented any Monsters below Rank A from approaching him. Thus, only Rimuru - that was over rank A upon birth - was able to do so without being hurt whatsoever. Rimuru commented that if the unrestrained Veldora were to unleash his aura outside, "more than half of Tempest's inhabitants, would be killed instantly".

There is also the Skill "Demon Lord's Haki" that mixes the user's aura with the user's Magicules, making the effects of the user's aura more potent. It's made from the combination of the Skills "Coercion" and "Magic Aura".

Inanimate Substances
Although Magicules is described as the building blocks of (magical/demonic) life, they are also capable of affecting inanimate objects as well. In most cases, only in regions with high Magicule concentrations, such as; the Sealed Cave and Rimuru's Stomach, inorganic and inanimate substances can absorb Magicules to become a magical substance, such as Magisteel.

In such cases, the substance remains an inanimate object but obtains features similar to that of organic matter, such as reshaping according to the user's will, etc.

Monster Rankings
In the Central World, Yuuki Kagurazaka created a system of ranking monsters according to how much Magicules they possess and how intelligent they are. The higher their Magicules, the more dangerous the creature is, and thus the higher the ranking.

Trivia

 * Magicules are analogous to "Mana," or "Magic Points," or "MP" in games and other shows; however, Magicules are more accurately represented by "Magic Power" than "Magic Points".
 * The term "Magicule"; is derived from "Magic" and "Molecule"; it should be noted that the term's Kanji itself; is referring to a magical/demonic Chemical Element or Atom instead, so describing it as a Molecule might be considered a mistranslation by the official translators. In addition, the Kanji being translated as "Magical" could alternatively be interpreted as "Demonic" as well; which is why Magicules are usually associated with Monsters.

pt-br:Magícula Магическая Энергия