Agender!Garrus
For years, zie doesn't question that zie is male. Of course zie is a guy - if you're not a woman then what else are you?
But, zie prefers to consider zier position in turian and other society as "C-Sec Operative" rather than "male Turian". Gender never seemed particularly relevant when you're pointing a gun at a criminal's face.
When zie leaves C-Sec, frustrated at all the bureacracy (zie can't help but noticing there are an awful lot of forms to go through if you wanted to change your name and pronoun designation), zie encounters ... a wider range of people. Most mercs, yes, that zie does not talk to further than to ascertain that they are the ones zie is hunting. But others too; there's a much wider range of expressions on Omega than there is on the Citadel. Counter-culture and all that.
When they assign zem the name "Archangel", zie is pleased. An avenging archangel, protector of the weak, righteous justice made flesh. There is something more, also. Angels are genderless, and Garrus likes that. You cannot assume an angel's gender from looking at them.
Of course zie brushes it off, liking the name, whenever anyone asks, including Shepherd when she find him. It was just a name the mercs him zem, nothing more.
As it turns out however, getting hit in the head and almost bleeding out does a lot to change your priorities. Maybe something was knocked loose, some long falsly-held beliefe about gender, but when Garrus leaves the medic bay the pieces begin to fall into place. Long hours spent along running calibrations down in the main battery gives one time to think.
And when zie comes out, Shepherd is the first one zie tells. There is some confusion at first - gender studies is not one of the classes offered when you're trained by the Alliance military - but some explanation clears things up nicely and Garrus feels a lot more confident in telling others. A note his made on his file, and Kelly sends a memo round, and people just start referring to Garrus by zie.
