Ihuarraquax is a young pure white unicorn who wandered the Korath desert with Ciri for a few days. She saved him after he was poisoned by a sand monster by using the Force found in the element of fire, something Yennefer had expressly forbidden her to do. When they met, Ihuarraquax was really only a colt and Ciri named him "Little Horse".
Between them, they were able to find food and water for each other and likely neither would have survived the desert without the other.
|“|| Several paces in front of her stood a horse. She blinked. It wasn't an illusion. It really was a horse. A young horse, not much more than a foal.
She was now fully awake. She licked her cracked lips and cleared her throat involuntarily. The horse jumped and ran some distance away, its hooves grating over the loose stones. It moved very strangely, and its coat was also unusual - neither dun nor grey. Perhaps the effect was just an illusion, created by the sun shining behind it.
The horse snorted and took a few steps towards her. Now she could see it better. Well enough to notice, in addition to its uncharacteristic coat colour, the strange peculiarities in its build: the small head, the extremely slender neck, the very thin pasterns and the long, thick tail. The horse stood and looked at her, holding its muzzle in profile. Ciri let out a quiet sigh.
A horn, at least two spans long, protruded from the horse's domed forehead.
— pg(s). 269-270, Time of Contempt (UK edition)
Ciri was reunited with a now fully grown Ihuarraquax, though she continued to call him Little Horse. He helped her escape the clutches of Eredin and the Dearg Ruadhri. The unicorn appeared also after Geralt and Yennefer's death, helping Ciri to heal/resurrect her adoptive parents and transport them to Malus Island.