Unknown World (current)
The Ancients (古代人 Kodaibito) are angelic creatures that lived on the Earth before humans took over their role as the most dominant species.
The Ancients are a species that lived millions of years ago, long before the humankind rose. But after humans' appearance on Earth, they had to retreat. Their emperor did everything he could to save the Ancients from their destruction but lost all his power in the process.
They enthrusted Fuku with the task of protecting the fossil of their emperor and revive him as soon as possible. They are only briefly seen when they take Mikeru with them, and in the anime, their images are hidden in the light.
The Ancients are angelic, not-living creatures, so they are probably spiritual, not physical beings. They have two pairs of wings. They appear in a bright white orb in the anime, and only as vague silhouettes in the manga. They wear clothing in similiar style to Mikeru.
The Ancients are known to be a powerful and mysterious species, and they have are very loving and forgiving behavior. Even now the light of their love shines brightly in the hearts of humans, Mermaids, and Panthalassas. They are long-lived, but not immortal as they had to "leave" Earth to make place for the humans. Their emperor, however, might be immortal as Seira stated that Mikeru had a heart that was saddened and frightened by the destruction of the Ancients, trapped in a cold, lonely fossil for tens of thousands of years. However that might be the effect of him, trapping himself in a fossil and it is unknown if he could be alive now without being trapped in it.
Although the Ancients are very loving and peaceful species they have powers that seem to be deadly, like Mikeru's power of absorbing members of any kind of species, in order to gain their life energy and become more powerful. Mikeru could also create demons from every kind of animal, with powers that even he hadn't demonstrated.
Mikeru had also an alter ego, Mikaru. That means that they had two bodies sharing a single soul. It is unknown if all the Ancients have an alter ego like him.
- Mikaru Amagi (she became an Ancient, before her absorbtion)