Naturers are a higher-order group of beings in which the very nature and concepts that constitute IDET have taken form as conscious entities. They are existences in which a concept that genuinely exists on Earth has manifested as a distinct individual — and every Naturer that comes into being in this way possesses self-awareness.

Each Naturer presides over a single concept — ranging from tangible natural phenomena such as fire, water, wind, and earth, to abstract concepts such as flow, time, death, and emotion — and is organically connected to that concept. Based on this connection, each Naturer possesses a unique ability rooted in the natural phenomenon they are responsible for. (For example, if the ocean exists on Earth, then a god of the ocean exists as well; and that god is able to wield abilities related to the ocean itself — waves, water temperature, and so on.)

Naturers may exist purely as the concept they embody, or they may take on a physical form by manifesting as a living being. When manifested, they possess a physical body, though whether their internal organs function normally remains unknown. The bodies they inhabit vary widely in appearance, and Naturers do not experience physiological needs such as hunger or the need for sleep. Naturers also follow the principle of creation and dissolution. If the concept a Naturer presides over disappears entirely from Earth, all Naturers connected to that concept cease to exist. (As one example, even if a concept has vanished from the human world, as long as that concept still remains within IDET, the corresponding Naturer will not dissolve.)

Naturers form a higher-order conceptual group encompassing gods, spirits, and fairies — and only these three species belong to the Naturer category. The distinction between the three is determined by the scope and specificity of the concepts they govern. Naturers who govern broad and overarching concepts are classified as gods; those who govern more subdivided concepts are classified as spirits; and those who govern extremely minute and limited concepts are classified as fairies. This classification is fixed from birth — there is no transition, promotion, or demotion between gods, spirits, and fairies. The primordial gods were created directly by ID, whereas Naturers who emerged afterward arose naturally through the flow of the natural environment of Earth that ID had fashioned.

Among Naturers, an invisible hierarchy appears to exist, based on ability and strength. Some Naturers stay close to one another like family and may even resemble each other in appearance — but Naturers do not form relationships through blood ties. (When certain Naturers appear to be like family, it is simply because they share a very close bond with one another.)

The Livings correspond closely to what we know as "living beings." They sustain themselves by maintaining their life force, and they are subject to the concepts of birth and death.

Unlike Naturers, which comprise only a limited number of species, the Livings encompass an enormous variety of species. As one of the products of nature, the Livings as a whole exist under the care and protection of the Naturers. Some among the Livings are also brought into existence through creation by a Naturer. Although the sheer number of species means that differences between them are significant, within IDET the Livings coexist in harmony — without the kind of rigid hierarchical structure seen among Naturers.

While each Naturer possesses a unique ability with characteristics that differ from individual to individual, the "abilities" of the Livings are not predetermined and vary enormously from person to person and from species to species. Some individuals possess skills that function as genuine unique abilities, while others have abilities closer to a natural talent, and some have no abilities at all. (In character profiles, all of these are referred to simply as "ability," without distinction.)

There are occasionally Livings chosen to serve as subordinates to a god. In exchange for following the god's commands for the rest of their lives, they are granted the god's authority — resulting in a dramatic enhancement of their physical capabilities and vitality, bringing them close to a state of immortality. These individuals are known as "Guardians of The Gods".

One defining characteristic unique to IDET is that, because it is both a part of Earth and a space separated from the human world, non-human species make up the vast majority of its population — and under normal circumstances, humans do not exist within IDET. As for beings such as extraterrestrials who have entered IDET from beyond Earth, nearly all of them are classified as the Livings.

Other Species refers to species that do not fall under the characteristics of either Naturers or the Livings.