Her intellect, wit and creativity must match his exactly.
Also, the Ninjette will always support her Ninja without fail through life.
Each Ninja only has one Ninjette and will never find another. Also, no true Ninja will ever be totally happy going through life with any woman other than his Ninjette.
Wow, Ninja John seems sharper and more deadly than ever, what do you think happened?
Answer from somewhat enlightened ordinary man #2:
He found his Ninjette and is now complete.
2) Sometimes ignorant people like to call themselves ninjettes to make themselves sound more awesome.
Person 1 "Man did you see that ninjette pay for his burger?
Person 2 "Yeah, they scare the shit out of me."
Miranda-Blah Blah Blah My names Miranda and i think im an awesome ninjette!
Billy-Miranda, your full of crap and not the least bit intimadating.
Miranda-Shut Up Billy! I'm gonna take you lunch money!
2) A female who believes she is a ninja, or engages in ninja-like activities (i.e.: judo-chopping, sly ninja-kicks).
3) The women crazy enough to hang out with the "Kung-fu Hillbilly," as seen on YouTube and Jerry Springer.
Normal person 2: "That's definitely his ninjette. You can tell by her headband that matches his costume."