The notion that a fox grows in power as it ages, until at last it casts off its very form, can be traced back to the old Chinese book of marvels, the Xuanzhongji^[2]. There it is said that a fox can turn into a woman at fifty years, into a beautiful woman at a hundred, and commune with heaven once it has passed a thousand. Carried to Japan, this idea of “rank rising with the years” grew into the view that sorts foxes into Tenko, Kūko, Kiko, and Yako[3].

It was the essays of Edo scholars that set these four ranks down in writing. Minagawa Kien’s Yūhisai Sakki^[1] first recorded the order, after which Asakawa Zen’an’s Zen’an Zuihitsu^[4] and Tachibana Nankei’s Hokusō Sadan^[5] carried it to a wider public. Within this scheme the Kiko sits between the flesh-bodied Yako and the Kūko and Tenko, who have all but attained the realm of the immortals.

Like the Kūko, however, the Kiko has left behind almost no concrete legend bound to a particular shape or incident. This is because the Kiko is less a single, specific creature than a name marking a grade — “a fox of about this rank.” When folk tales speak of fox-possession, the culprit is sometimes called a mere Yako, and sometimes a Kiko that has gained a further measure of power — and it is in such tellings that the outline of the Kiko dimly takes shape.