How do I wear costumes?

I know it sounds like an obvious question, but the obvious didn't work. I'm assuming I got this "Gavi Regan" set through those recommendation letter thingies, buuuut... right clicking the item pulls up a context window that says if I equip the item then it can no longer be put on the market. Upon pressing Enter.... nothing happens.
There doesn't seem to be any requirements to wearing it in the item descriptions other than the words "Ninja Exclusive" I mean, I am playing as a Kunoichi, and a kunoichi is a female ninja, ere go I should be able to wear it. So what's up?

Does Kunoichi not count as a ninja or did someone drop the ball and mess up class rewards?

 

Gavi Regan Armor is Male only (Berserker, Wizard, Musa, Warrior, Ninja) which means you can't wear this costume as Kunoichi but you will be able to wear it with Ninja.