The Kah'Nath are the ruling regime of the land in which Ren and her family live. It is not yet known if their influence extends across the entire land of Alathia. A group of Kah'Nath soldiers, led by the Commander, is prominent in Series One.
"They are the Eye of Justice and the Mouth of Truth." - Ren, Episode One
The group seem to be a military, religious and political ruling class. The primary function of the Kah'Nath seems to be largely militaristic; the order of soldiers 'keep in the peace' in villages and towns, arresting miscreants like Hunter and hunting down Mahri'Rai and Marked Ones.
The Kah'Nath seem to hold a totalitarian authority over the people of Lyngarth, able to dispense martial law and condemn people to death without trial. They operate out of a castle type building in Lyngarth, in which there is a gaol, operated by dedicated gaolers.
It is likely the Kah'Nath also hold all the primary political roles in the land, as no other ruler is seen in Season One. A Kah'Nath teacher is seen in Lyngarth, and Baynon mentions being taught about glorious Kah'Nath victories in their lessons.
The Kah'Nath clearly condemn everything associated with the Nu'Mahri and the Mahri'Rai, referring to the spirits and their keepers as 'Underly Magic'. The Nu'Mahri and the Mahri'Rai are treated as fugutives and anyone found harbouring Marker Ones will be punished.
At the beginning of the Series, Ren has a book which Karn has given her. Dagron points out that books are forbidden and she will be in big trouble if caught with it. The reason behind this ban is not known, but it may be due to the control of education.
The Kah'Nath soldiers wear a distinctive uniform, formed of black lamellar breastplate, black trousers and red tunics, marked with the logo of the Kah'Nath. They wear helmets with a tall red plume.