The aeon are essentially god-like beings who cannot die. They possess incredible reviving abilities that prevent their bodies from being completely destroyed, and an organ called Mandorla, which are wings that can come out of an individual's scapula through a gap on their shoulder blades. They are capable of reproducing through parthenogenesis, as evidenced by Terumi's pregnancy. They also have a very high sex drive, although they are not able to procreate with other humans.
All facts known about the aeon were discovered through laboratory observations and experimentations on Terumi (referred to as the "Original One"), and her son, Shūji, during part of his childhood. Similarly to other creatures, the first aeon was born from Harthatenarl because of the incorrect separation and healing of one of her body parts.
While Harthatenarl herself and the Original One are distinct beings with their own abilities, they also share a few characteristics. They are both immortal from humanity's perspective, have absurd strength as well as full control of their brains and are capable of mutating their appearance from seemly humans to eldritch forms.
However, there are several features about this race that far deviate from the normal. It is unknown why Terumi's traits such as physical mutations are not passed down to her offspring, or even if Terumi has an actual gender at all since she was able to have triplet sons despite being thought to be a female and able to get pregnant. Terumi's gender issue is further made more complex by the fact Terumi can change her human gender to that of a man or non-binary.
The only known aeons are all shown to completely lack pigmentation in parts of their bodies, as they have completely ghastly white hair and skin, purple tongue and mouth, small fangs, and reddish, pale eyes from birth. They are often compared to ghosts, angels and even stars. In addition to that, they have small openings on their shoulder blades in which they can sprout two other limbs from. These limbs form webbed wings that extend themselves according to the individual's height, are overall near transparent in appearance, to the point it's possible to see their veins, and are connected to their spinal cord.
So far, Terumi is the only aeon capable of changing her physical appearance to any other form, including to her original one. While she does appear as a human and her sons all follow the same, she can either assume the appearance of any other human or revert back to a dragon-moth hybrid which is believed to be the form she took when she was born from Harthatenarl's body. Her sons can also transform into reptilian-like beasts, although the process occurs differently compared to Terumi's.
While Terumi can morph into any creature by simply altering her body shape, her children first had to undergo a process similar to moulting; their internal organs, muscles and other organs such as their eyes turn into a viscous, transparent substance when they cast off their skin, and it sprouts from within while giving color and form to their true appearance. That fluid is actually alive and sentient; it quickly hardens when out of the discarded human cocoon, forming a new body. When reverting back to their human form, they shed their scaled skin and emerge from a crack in the back, in between their wings.
Aeon (or æon, Greek αἰών) means "age", or alternatively "forever" or "for eternity".
In Gnosticism, aeons are one of the known names for the various immaterial emanations of God, in which they are spirits, spheres of being or a series of extensions of being that emanated outward from a common source — the godhead —, being attributes of the nature of the absolute. They center around the concept of Gnostic dualism, that dwells on the conflict between matter and spirit.
The first aeon (One) originated from the unmanifest divinity and was said to be charged with a divine force. Successive emanations of One were charged with successively diminished force and rose outward, in which One serves as their source. Upper aeons are extensions of the One’s unity, as well as are said to have been created when the One reflected upon itself, while lower aeons imitate upper ones.
Aion is the name of the Hellenistic god of time and the zodiac. He is often contrasted with Chronos as he is associated with eternal and cyclical time, while Chronos is the personification of bonded time, divided in present, past and future. Aion is often imagined as a nude or seminude youth (though he has also been depicted as an old man) within a circle representing either the zodiac or ceaseless time. He is associated with ouroboros, as it represents the cyclical nature of the year, and a serpent that hides its tail under the rest of its body, although those two may overlap.
Aeons are also a number of summoning creatures in the Final Fantasy series. They are the fayth's (humans whose souls were willingly sealed in statues, thus remaining in a dreaming state) dreams, similarly how Gnostic aeons physically express a deity's essence rather than their temporal bodies.
The aeons are primarily based on ghosts, in particular their color scheme.
The three sons' transformation process is based on that of snakes and moths.