The world where the story of How to Kill an Isekai Protagonist takes place (Velisadia). At one point, the Demon King ruled the whole continent, but after the mage-heroes defeated him, they split the continent into four domains. Necromancer took almost half of the country but most of it is a frozen wasteland and sparsely inhabited. Druid took a smaller, secluded area for herself. The country is mostly closed off from the rest. Warlock and Mentalist split the most fertile and most populous part of the continent. Main character currently lives a quiet life in the capital of Warlock's country (Kamenar).

Excerpt from Encyclopedia magicka

"Everything in the world is made out of energy. Even matter is made of different types of energy interacting together. There are six types of energy responsible for all creation and destruction in the universe: life, earth, water, death, air and fire. Magic is a phenomenon available to some beings through which they emulate similar processes that occur in nature. Given enough energy, one could create everything in the universe, even a whole planet. This remains highly theoretical as the amount of necessary energy would be astronomical. To distinguish between all of the energy in the world and specific energy that is used to perform magic, the latter will be denoted as magical energy, even though there is no qualitative difference between the two. The process of manipulation of magical energy is called a spell.

"Six types of energies and their relationships"

"On Antipodes and Prevailers"

"Antipodes and Prevailers are two concepts about energy that are most often misunderstood. Antipodes is a classification of energy based on opposite qualities. There are three pairs of antipodes: Air-Earth, Fire-Water, Life-Death. These energies can not coexist together. Spells of equal magnitude from antipodes will nullify each other without effect. On the other hand, prevailer is a ternary relation of a cyclic power order of different energies. What this means is that every energy has exactly one prevailer and prevails over exactly one other energy. If an energy prevails over another it means that when two antagonistic spells of similar magnitude confront each other, the spell with the prevailing energy will always overpower the other. One way to illustrate this is: Life cracks Earth, Earth absorbs Water, Water purifies Death, Death corrupts Air, Air suffocates Fire and Fire consumes Life.

"On apeirons"

"In order for a spellcaster to use magic he needs to sap from a source of magical energy. Sources of magical energies are called apeirons. If an apeiron doesn't have energy associated with it yet it is called empty or void aperion. Beings that are born with aperions that are already associated with a magical energy are called magical beasts. Humans are born with thirteen void appeirons. This means that humans are weaker than magical beasts at first, but leaves humans with a greater flexibility to develop.

"Example of a mage with one death exoaperion, one earth exo and one endoaperion, two fire endoaperions, and eight void aperions"

"With regards to the spellcaster's body, aperions can be further classified into exoaperions and endoaperions. There are seven exoaperions and they are located outside of the body circle. Exoaperions are responsible for the spell's power and range. Endoaperions are located in the body and there are six of them in humans. Endoaperions are responsible for control and longevity of the spell. A novice mage is advised to start with endoaperions, because when the energy is pulled only from exoaperions, the spellcaster can not control the spell and it could get cast in any random direction, even upon the spellcaster himself. With only endoaperions caster would only be able to cast spells in touch range however, so eventual mix is advised."