To start this, I feel like pointing out that Zhanbun gender is not native to the Zhanbun (which I tend to call zhan so I'll do that here). The zhan originally didn't have a concept of gender inscribed in their society, it came to them when some people got obsessed with media from other cultures and from other ages. To make it more analogous to our society: In zhan society, gender is a weeb thing.
Also they're post-scarcity transhumanists on the year 2500, which also has an impact in how their ideas developed here.
So, it originally started with three labels: baoq, zaeq and daaq. These roughly translate to female, male and non-binary, respectively. They didn't have a native intuition for what these labels mean to us, and those who were invested in the history of gender didn't particularly enjoy the concept, so they just went with whatever felt right.
A thing to point out though, daaq, just like non binary, is an umbrella label. It's a slightly different one for two reasons:
Xaiq is another umbrella label that is roughly equivalent to xenogender. It's people whose gender doesn't allign with baoq nor zaeq, and it's not defined by the presence or lack of those. For example, if someone said their gender was ran (fire), they would fall in the xaiq label, not the daaq one. The way the word non binary works, we'd see xenogender as a label within non-binary. This is not how it works for the zhan.
And the other reason:
See, in our society, gender is kind of the default. I mean, at birth the doctor screams "its a boy!" or "its a girl!", and I don't actually know what happens when you're intersexual. Huh.
But this isn't the case to the zhan. Like I said, for the zhan, gender is this weird thing the weeb kids are into. Not everyone has heard of gender and not everyone wants to participate in it.
There's a word for that: gauq
It's easy to translate gauq as agender. But there's a subtlety there that doesn't translate well. Agender is, at least for most people, opting *out* of gender. A zhan who is not immersed in our history would think of agender people of daaq (or xaiq), not gauq.
To put it simply: agender is an empty box, gauq is the lack of a box.
Here's the flags