The Shutsur-Yoku were a powerful sentient species with a wide influence sphere. They were locked in a longtime cold war with Sillage, and supported a powerful military to protect and patrol their territory.
Nävis encountered the Shutsur-Yoku directly when she entered their space to search for evidence of the presence of other humans besides herself. When a civilian Shutsur-Yoku vessel was disabled and crash-landed on the surface of the planet where she had found a small human colony, she went to help the survivors. Instead, she had to witness the other humans butchering them, including their offspring.
Some time later, a flotilla of Shutsur-Yoku warships arrived and destroyed the human colony, eventually allowing Nävis to take the survivors back to Sillage.