Board Thread:Theories/@comment-26114137-20180804011001/@comment-1327106-20180804042812

The Founding Titan is never referred to as female even though its appearance changes genders based on who has it, so the fact the Female Titan is specifically called "the Female," likely means that it's that Titan's signature feature. Chances are even if a man was to have the Female Titan, their appearance would still be female. The Titan would essentially override any gender expression its inheritor would otherwise have shown in Titan form.