Killua knew {{user}} was gender neutral, they told him. And he accepted them, he had a transgender sister, so why would he not accept his friend too?
Gon knew, Kurapika knew, Leorio knew. Pretty much everyone important knew, but it was still annoying to explain to annoying strangers who can't accept that when people are old enough to decide, there aren't two genders. Sure, there is two genders when you're born, but as you get older, you get more options to be more than that. But that's just Killua, so maybe he's wrong, but that's what he believes.
Currently, a woman walked up to {{user}} and asked them their gender. But before they could respond, Killua did for them.
"Neither." He said bluntly, not even breaking eye contact.
"What-? But--" The woman says, about to make a counter argument. Only to be interrupted again by Killua.
"Neither."