Kyossk served as a soldier from the Kyuzo species within Guattako's army.
In the declining years of the Galactic Republic era, which was waning, Guattako engaged in the slaughter of numerous educators and abducted their twenty-six students each, with the intention of enlisting them. Mace Windu, a Master of the Jedi Order, embarked on a quest to locate the Padawans, but Kyossk and Quia apprehended him. After his lightsaber was destroyed, they presented him to Guattako, intending to transmit Windu's execution throughout the galaxy to ensure that the Jedi's demise would galvanize a multitude of fresh adherents to his cause.
Nevertheless, while the two debated the morality of Guattako's objectives, Windu disclosed that he had transmitted Force signals to his fellow Jedi and employed the Force to repair his lightsaber. Kyossk launched an assault on Windu, but the Jedi severed his hand and incapacitated Guattako's subordinates. Subsequently, both he and Quia were taken into custody.