The Kai Ken(甲斐犬?, also called the Tora Inu or Tiger Dog) is a breed of dog that hails from Japan where it is a natural monument and has been bred for centuries. It is an extremely rare dog even in its native land and is related to the Japanese Spitzdog type.
The Kai Ken is a medium sized dog with a wedge shaped head and prick ears. Males are typically 18 to 22 inches at the shoulder, while the females are slightly smaller, 17 to 20 inches at the shoulder. The tail may be curled over the back, or carried in a sickle position. Limbs should be strong and hocks should be well developed reflecting the dogs’ history of mountain life. The coat is of harsh texture, medium length, and comes in various shades of brindle (tiger stripes). The red is the Aka-tora, the black is the Kuro-tora and between them, the Chu-tora. Puppies are born a solid color and their brindle markings develop as they age, sometimes taking as long as five years before fully showing.
The Kai Ken is intelligent, agile, alert and brave. They are natural hunters and make good watch dogs, being reserved with strangers but loyal to their families. They are friendly, often good with children and are not usually aggressive towards other dogs. Many love to swim, and have been known to cross rivers and climb trees while chasing their prey. 
The Kai Ken is considered 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 were used to hunt boar and deer. This breed was designated a natural monument in Japan in 1934.