Our world, an indefinite year far beyond ours. Other mammals evolved greatly and they changed, intellectually and physically, to adapt to the human ways of living. But these mammals, known as the dōbutsu-hito, want social space that humans are not willing to share: this brings a rupture between the two races, and political, ethical, and moral issues arise. Humans build great colonies surrounded by tall walls to retreat themselves into and shut the other mammals out.

It is in this scenario that a human who never saw a dōbutsu-hito in person before starts to feel the changes of being immersed in a world humans excluded themselves from since a long time ago: life.