Don't take the heading too literally, in reality, we actually want to see everybody vs. everybody, but in this case we're referring to Arya Stark as a Faceless Assassinm, returning to Westeros to wreak total havoc. Her character has been built up for so long that time is running out for the pay-off to be spectacular. She needs to wrap up her training this season and make a move back to the main fold. Her progression has been accidentally killing a boy, to purposefully killing in defence, to assassinating the horrific Meryn Trant. Now she needs to go out and eliminate a character people actually care about. She could make a move to King's Landing, she could make a move for the Wall, or she could land anywhere between, but when she does, we need to start seeing some serious ass-kicking for Arya's whole character to be worthwhile.