Kurotaiyo no sekai is the world of the Black Sun, world of boundless desert consisting of ashes. But it's not so simple as it seems at first sight. This world is like a mirror, if may say so. It has two kinds of inhabitants: Kurosagi are black hares and Chokusagi are blank hares. Kurosagi contain Vital Fluid. It allows them to see the inaccessible essence of this world (reflection): see the life that fills this world, creatures and beings that inhabit in it. Vital Fluid also gives Kurosagi immortality and protection from the Black Sun. Chokusagi deprived of vital Fluid. They see nothing but desert and don't feel anything except scalding Black Sun. Their sole purpose is to find and take away Kurosagi's Vital Fluid. After Chokusagi take away the Vital Fluid they will become Kurosagi and Kurosagi from which Vital Fluid be taken away becomes Chokusagi. After becoming Chokusagi theirs life become too limited. If during this period they won't find the Vital Fluid they will become ashes, part of the desert.

This picture shows the world such as it's seen Chokusagi.

Chokusagi see the sky and the desert in dark colors and the Sun is white. If Kurosagi look at this world (mirror) they see the sky and the desert in light colors and the Sun is black.