Karate Kid new costume.
This is one of my favorite stories featuring Duo Damsel. Not only is it a fresh use of her power, but we also get to see her great personal strength and loyalty.
I'm particularly impressed by the way she's drawn; when she enters, you're not even sure who she is -- then when you turn the page, she splits and gives that line "United I fall...divided we stand." Every time I read this story, that line gives me chills.
It's also a great example of the archetypal Legion story in which those with the greatest powers (Superboy) are useless, while the one with the weakest power (Luornu) manages to save the day. And she's not even an active Legionnaire at this point! That's a hero.