Gender locked race?

[Gwenorai]

Some prime Waifu Material Here:
Tomamo no Gozen, Suzaku, Ultima the High Seraph, Tioman, Twintania.

And these are just off the top of my head. Easy to make your point when you just ignore all the examples that blow it out of the water.

Suzaku has a wifu form, Tomamo No Gozen has a wifu form, and Ultima the High Seraph also has a wifu form - check ff12.
Dragons don't count they're fully 'beast like'...unless you're into that thing.

Note; the fate 'Foxy Lady' she spawns as a female au'ra with fox ears before she turns into the ninetails; when she's defeated she reverts back into that form.