Water or Blood
The northern border of the Empire is the Ice wastes and its peoples who travel across the wastes to strange places past the ice call themselves Icewalkers, but they are called Savages in the Empire. They honor strange nature spirits and live in small mobile family bands.
There are a few trading outpost like villages at the border of the tundra where Kratian and Gethenomite merchants trade with these people for the oddities they bring across the wastes.
They travel in small caravans and bring strange treasures from the far north, from the other side of the cold. they will exchange these for many southern goods.
Their myths involve some great dread ruler who conquered all the earth and then ascended to godhood by becoming death itself, and in doing so broke the world, Requiring all the other gods to assemble and imprison him on an icy throne, frozen their for all time, and never allowing the wastes to thaw.
The highly educated may also know Geth has a similar myth about Death ruling the world to then be overthrown and cast down into an icy throne, but their myth has deaths sons (litches all) fleeing the terror of the gods to found new kingdoms.