Poor Arya has been through a lot in her quest for vengeance. At the end of Season 5, she lost her eyesight and ended up a beggar on the streets, which is where the start of Season 6 found her. In Episode 3, she finally got her eyesight back after passing numerous tough, painful tests. She endured beatings, endless questions that seemed impossible to answer, and lots of intense training, but it finally seemed to have a resolution in tonight's episode. How did Arya Stark get her eyesight back on Game of Thrones?
As the waif beat her once again (could that girl chill on hitting Arya with the huge sticks, please?), Arya revealed her family history and the people on her kill list. The waif seemed to know when she was lying, hitting Arya when she said she had four brothers instead of three; Jon counts as a half-brother – or maybe a cousin? Arya's list of those to take revenge on was short but sweet: Cersei Lannister, Gregor Clegane, and Walder Frey. Most notably, Arya spoke of herself in the past tense, showing her commitment to becoming one of the Faceless Men and giving up her identity.
When she is finally able to block a hit (still blind!), the man who wore Jaqen H'ghar's face took her aside. He said that he would give her eyes back if she told him her name, but Arya remained firm, saying only, "A girl has no name." It seems she has truly given up her identity as Arya Stark so that she can fulfill this journey. The man seemed satisfied, and he scooped some water out of the pool in the hall of the House of Black and White.
Arya hesitated, and with good reason. The water in the pool is poisoned, usually given to those who want to die. But as Jaqen (or whoever) tells her that if she's truly no one, she has nothing to fear. Arya takes him up on that double dog dare and slurps down some water. She closes her eyes briefly, and opens them to find her vision restored. When asked who she is, she replies, "No one."
It's definitely a new turn in Arya's – er, No One's story. She has always been single-minded in her journey to strike back at those who hurt her and her family, but this is on another level. She's letting go of everything that made her who she was. Whoever she is now, she's not Arya Stark anymore.