Sigma (Sky) is another clone officer in that evil ol' empire. (Geeze... I make it sound like Soviet Russia... >_>)
Sigma, unlike her "sisters" has no supernatural powers, however, she does have abnormally fast reflexes, and can come out of tight situations (that is, if it involves guns or close combat) The fact that she can do this well without any "super powers" only makes her more badass.
She's more than likely second to best on the Empire's list. (Her older "sister" Omega is top)