The Kai Ken is considered by some to be the most ancient, and purest dog breed in Japan. It was developed in the isolated district of Kai (Yamanashi Prefecture) as a hunting dog. Kai's were used to hunt everything from boar, deer, bear, to pheasants. This breed was designated a natural monument in Japan in 1934.
Kai are also known as the Tora-inu or Tiger dog because of their brindle coloration. They come in three shades of brindle, Aka-tora (red), Chu-tora (medium), and Kuro-tora (black). The majority of Kai seen today are Kuro-tora primarily due to their popularity in the show ring. The resulting decrease in Aka-tora bloodlines has been noticed, and efforts are under way to preserve them.
The Kai is a medium sized dog with a wedge shaped head and prick ears. The tail may be curled over the back, or carried in a sickle position.