Ko is the gender-neutral pronoun that quigutl use for each other. Unlike other pronouns (she, he, etc.), ko does not change into different forms.
Tess does not use ko for Pathka, Kikiu, or any of the other quigutl that she encounters, but she does use it, in retrospect, for Saar Spira, who has Tathlann's Syndrome, making them neither male nor female. However, most people use he/him pronouns for them or call them "it."