Kuda-kitsune or Kanko is a creature supposedly employed by Japanese kitsune-tsukai, those who use foxes as spirit familiars. Its use is described in various books, as follows:
In the Sōzan Chomon Kishū the kuda-gitsune is described as a rat-sized fox which can be kept in a pipe.
According to the Zen'an Zuihitsu the kanko is a fox the size of a weasel or rat, with vertical eyes and thin hair. The magic-user summons the kanko to appear inside a bamboo pipe he is holding, whereupon the fox will answer all the questions it is asked. The origin of this practice is traced back to a yamabushi who obtained this art while undergoing strict asceticism on Mount Kinpu. These Kanko are said to be numerous in the northern mountains of Suruga, Tōtōmi, and Mikawa Provinces.
Researcher Inoue Enryō in his Yōkaigaku Kōgi, quotes a newspaper article regarding the kanko, in which it is a tiny, mouse-sized creature which hails from Shinano Province. It is named for its tail, which is like a pipe cut in half. It can be tamed and kept in a pocket or sleeve, and uses its supernatural power to seek out assorted information which it then whispers to its master. A person who keeps it is thus able to see into both the past and future.