Another reference page for my hellaverse s/i! I'm going to do this for a few of my self-inserts, so if there's anyone you're interested in, let me know!
I headcanon that some hellborn species are more complicated in biological sex than others, and succubi/incubi are very much on the complicated side of things, with six gender options. Echo is "fifth gender" but uses nonbinary terminology because they grew up in Pride, with mostly Sinners and Imps. (Sinner sexes can also be tricky and unique, but there's so many options that they've mostly circled back around to binary labels for simplicity)
Tends to wear tight dresses on the job, tight pants and shirts when out with friends or shopping, and wears the baggiest clothes around the house when there's no one there to see them. Succubi can naturally shapeshift between human and demon, and this self-insert holds an in-between appearance when they're out in public with all their favourite attributes of both forms.
(extra frame about sexuality under the read more!)