The Korou (虎狼 lit. Wild Beast) are a race that live in another world parallel to that of the shinobi world called Tenchikaimei. Though they too have a shinobi system, the main difference between the two is that this race is united throughout their land, unlike the humans of the shinobi world.
Originally the Korou were humans with a Kekkai Genkai that allowed them to take on traits of animals and use their abilities temporarily. At this time many didn't know what a Kekkai Genkai was and when it was demonstrated in front of ordinary people, many grew fearful and attacked them.
The humans with the ability didn't want to start a war and faded into the shadows. However it was already too late, and soon hunts were made against them. Slowly they were massacred, until eventually they totally became beasts, and could take on a human form and a beastial form. Wishing to escape they fled into the wilderness, learning the ways of the animals over time. During this time the people began to call themselves the Korou.
However, at the beginning of the shinobi era, the shinobi somehow learned of the Korou's existance and still ignorant of Kekkai Genkai, slaughter numerous innoccent animals in an attempt to exterminate the Korou. The Korou couldn't bare to have the animals, many which were their friends and allies killed because of them, and wove one of the first time and space jutsus to escape into another dimension.
Once there they began to settle down, continuing their former way of life, as beasts, and humans. Over time the Korou began to call the world, Tenchikaimei and have lived in peace for the most part since they left the Shinobi world.
The Korou have a shinobi system, but have a united civilization. They are as advanced in technology as that of the Shinobi world, but are more nature bound than they are, not being wasteful and destructive with the environment.
The shinobi system is used to help defend the land from raiders, and other rogues. Though wars are rare they have happened before, and are usually quite bloody, though order is normally restore shortly after conflicts subside.
The Korou do not have cities and houses, instead prefering to sleep as beasts do, using natural land forms as shelter when necessary.
The craftsman of the land forge their blades simply through chakra control manipulating the elements, this natural way of making blades has created some of the finest weaponry known.
The Korou are unique in that they have two forms: a human form and a bestial form. The human form is more for when they journey into the Shinobi world, but is still used in Tenchikaimei as well. The bestial form is more commonly used, and can be anything, from a creature found in the shinobi world, to an original beast.
Besides the form changing ability, which can be used at will, the Korou are known for swordsmanship, craftsmanship, and hand-to-hand combat prowess. Their hand-to-hand style is ruthless and involves the use of speed and power in aggressive moves and counter attacks. Their swordsmanship style uses the same concept, and their craftmanship is exellent, creating all sorts of useful, near unbreakable blades (in fact some actually are unbreakable).