The common enemy of all Game of Thrones fans; Night King was killed by Lady Arya. It is an unforgettable scene to all Game of Thrones fans how Arya jumped from behind the Night King and stabbed him into his stomach by the dagger which was given to her by Bran shattering him and the whole army of nightwalkers into pieces.
Arya never liked her to be addressed as lady Arya from her childhood and she had a good target even than Bran. She wanted to ride horses and fight instead of learning to sew as Sansa. From her childhood, it is Arya Starks determination to the best swordsman.
By seeing that and the needle (given by Jon Snow) after their arrival to kings landing Ned Stark (Father) hires Braavosi Syrio Forel to teach her how to fight. (season one) He there emphasizes how important it is for her to learn how to fight correctly.
According to latest theories, it says that Faceless Men used Syrio Forel to recruit Arya and then he used Arya as a weapon to kill The Night King. In Braavos Arya trains to fight with Faceless Men on how to kill. It can be seen as a preparation for Arya for later as she has to kill Night King in Season Eight.
According to Reddit user cheekyleaf: “Let’s say that Arya was relentlessly recruited by Faceless Men because they knew with their collective hive-mind that she’d be the one to eventually kill the Night King and end the long night.”
While they say so another fan suggests that “I don’t think that the Faceless Men ever intended for Arya to become one of them” They say that the Faceless Men selected Arya as their weapon of choice.
Arya saying that she is a Stark and she is going home is possible to be a coverup she says before she returns to Winterfell to hide her true intentions from us. What do you think?
 hires Braavosi Syrio Forel to teach her how to fight.){kind=link}