For a while now, it's seemed as though Arya Stark was the only true hero left in Westeros (and across the Narrow Sea in Braavos, for that matter), and was the only one we could count on to fight on the side of what is just and right. However, it seems Essos has more parallels to the real world than we initially thought, because lately Arya's fallen in with the wrong crowed — the Faceless Men, that is — and has started changing a bit. With nowhere else to go and no one left to turn to, Arya cashed in on the coin given to her by one Jaquen H'ghar last season and has since reunited with him in the House of Black and White. There, she's been learning to become No One... or, you know, a trained assassin. The recent revelations in regards to the real purpose of the Faceless Men, as well as Arya's willingness to go along with it, is more than a little concerning, I'd say.
Arya has always been a total badass, and that's why we've loved her. But her sympathies always seemed to lie with the underdogs — particularly because it's the underdogs who always seemed to be hard done by in the Seven Kingdoms. And while she has indeed killed before, it was more out of necessity and self-preservation than a desire for blood. But now that Jaquen H'ghar has her under his thumb and plans to have her "train" by assassinating someone via a lethal dose of poison, the stakes are much higher than they've ever been before, and Arya deserves more than the fate of becoming a murderer.
There is, of course, every reason for Arya to want to cast off the shackles of who she once was. Most of her family has been murdered or is otherwise lost to her, out there God knows where doing God knows what, and her last name alone is enough to end her life if she found herself in the wrong company. Also, being Arya Stark hasn't worked out all that well for her, generally speaking. She's never particularly felt like a noblewoman, anyway, so joining the Faceless Men is not only a way to escape a terrible past, but it's away to adopt a new future as someone completely different, and that's something no one could blame her for.
Still, to find her led blindly into becoming a killer just because she's a young girl that's suddenly so malleable would be a great disservice to the character of Arya Stark, who we've come to know over the past five seasons as a strong-willed, strong minded girl who doesn't just go along with the status quo because it's what's expected of her. Sure, she's bound to make mistakes as she navigates the world of growing up, and sure, anyone would get to breaking point after all she's been through over the past several years, but I still don't buy Arya as a cold-blooded killer, no matter if the Many-Faced God demands it or not.
We still have two more episodes to see which side Arya will choose in the battle between, well, good and bad, in so many words. We know she's hesitant about the orders given to her by Jaqen, and whether or not she follows his instructions to completion will determine a lot about her character — and likely, given who she's gotten herself mixed up with, about her life being in danger, because something tells me the Faceless Men won't take too kindly to someone they see as a traitor and a coward.