The last episode of Supergirl season 4, "Man of Steel," will cause major problems for the mysterious Russian Supergirl. Although she hasn't been seen the season premiere, this "Dark Supergirl" could well become Kara's most dangerous foe.
The season finale of Supergirl season 3 saw a Kryptonian pod crash-land in Russia, bearing some sort of Supergirl doppelganger. Set several months later, the Supergirl season 4 premiere revealed that this new Kryptonian is working with the Russian government, helping expand Russian power and influence across Eastern Europe. She was shown leading what seemed to be a Russian invasion of the fictional Eastern European nation of Kasnia. But, curiously, she hasn't been seen since. Russia appear to be keeping their Kryptonian asset a closely-guarded secret. Apparently, this is leading up to a story inspired by the popular "Red Son" Elseworlds comic.
All that's sure to change in the aftermath of "Man of Steel." In Supergirl season 4, episode 3, the entire atmosphere of the planet has been contaminated with Kryptonite. This had a debilitating effect on Kara, rendering her comatose and ultimately forcing the D.E.O. to place her in an advanced containment suit created by Lena Luthor. Superman is currently off-world visiting Argo City, so he's safe enough right now, but the Russian Supergirl will presumably be affected by the Kryptonite as well. More concerning still, the Russian Government may not know much about Kryptonite, and they have no idea the Earth's atmosphere has now been laced with trace amounts of the alien mineral. Their Supergirl will have just collapsed, and they'll have no way of knowing why, or what to do about it.
So what's going to happen to the Russian Supergirl? It seems unlikely that Russian scientists will be able to help her; even Brainiac-5 couldn't think of a way to save Kara using the advanced technology of the D.E.O. The Russian Government will only get a hint of what's going on when they see that Kara has donned a containment unit. The same technology could help their Supergirl, but first they'll need to acquire it - either from the D.E.O. or, should they recognize Lena's handiwork, from Lena herself. While the D.E.O. and Lena were willing to work together to help Supergirl, would they be willing to assist the Russian Government? And how will Kara respond to the news that she has a rogue doppelganger in Europe?
The Russian Supergirl has been one of the greatest mysteries of Supergirl season 4. Three episodes in, and the show has avoided revealing anything about her; she hasn't even been named. Hopefully the events of "Man of Steel" will force the show to shine a light upon her at last.
Supergirl continues next Sunday on The CW with "Ahimsa".