The Yari are a tribe of warriors for hire. Although they are native to Balor, they can be found fighting for either side. Gods and countries change over the years, and wars come and go. Yet all of them need soldiers at some point, and those soldiers need coin.
These simple principles both come from and define the Irumian soldiers known as the Yari. They serve only their own greater good, and obey anyone willing to give them coin for warfare. When Howlfang first began organizing the attack on the Vale, it was the Yari who sold their services to the Shadow. It was also the Yari that Gunther recruited for the attack on Fort Balor.
Despite being originally from Irum, anyone willing to obey the 'Rule of Gold' can be brought into the ranks of the Yari. Even non-human soldiers are welcome, so long as they can stomach turning on their own once the price is paid.