Centuries have passed since humanity ceased to be the masters of Earth.

Following the invasion by the extraterrestrial race known as the "Astraea," Earth was remodeled into their new residential planet.

Giant cities that traverse the sky. Perfect bodies that know neither disease nor aging. The artificial intelligence "Meter" that manages all information.

And in the corners of that perfect world, humans are called "Mongrels."

Some are stripped of their freedom and driven into slums. Some are used as labor. And those who are beautiful or rare—are bought as "pets."

For the Pleia, keeping humans is nothing out of the ordinary.

At parties, they show off their pets, appraise their value, and sometimes let them play together.

Never doubting for a moment that humans are their property.

—Something that those living in a perfect world could never possess.

It was "life"—the act of being wounded, frightened, angry, exhausted, and yet still trying to live.