The story is set in the future on the planet named Amoi which is controlled by a supercomputer named Jupiter. Among the mostly male human population, the blond-haired elite class is allowed to temporarily keep slaves as luxury pets. One elite member, Iason, encounters a lower class slum mongrel named Riki and decides to forcibly take him as a pet which is unusual and taboo in elite society. However, Iason keeps Riki longer than it is socially approved, and rumors abound about their possible relationship.

Publication note: The paperback editions are revised and greatly expanded from the original hardcover edition. The first paperback edition, from Seibidō Shuppan under their Crystal imprint, is incomplete, covering only six of eight books. The complete series was re-released by Tokuma Shoten in six volumes under their Chara imprint; the first four are semi-omnibus (books 1-4 correspond to Crystal 1-6) and the last two are the previously unreleased material. The English edition from Juné was originally based on the Crystal edition, and will have eight volumes (corresponding to Crystal 1-6 plus Chara 5 and 6).