A man must return. An Internet must get excited about it.
Eagle eyes over on Watchers on the Wall first noticed that Tom Wlaschiha, the German actor who played fan favorite Jaqen H'ghar on Season 2 of Game of Thrones, is listed on the cast list of an official HBO schedule for the upcoming season. Hooray!
But here's what is kind of weird about that: Last time we saw Wlaschiha's character, he was literally changes faces, as one of the perks of being a Faceless Man.
To recap, Faceless Men are a religious society of assassins who worship the Many-Faced God. After Arya saved Jaqen's life in Season 2, he "owed" her three lives, using his mysterious assassination training — and he quickly delivered.
In the Season 2 finale, Jaqen leaves Arya after she refuses to come with him to Braavos to learn the secrets of the Faceless Men, but he gives her a coin and tells her, "If the day comes when you must find me again, just give that coin to any man from Braavos and say these words to him: 'Valar morghulis.'"
So by using the coin and the words, Arya can find Jaqen again. Sounds straight-forward. Except that when Arya realizes she doesn't have enough money to buy passage on a ship, she hands over the coin to the Braavosi captain and says, "Valar morghulis." This exchange earns Arya not just passage, but the captain's own cabin.
It's important to note that in the books, Jaqen only vaguely promised help if Arya ever used the coin and the words, not his actual presence. Such a subtle, but meaningful deviation from the books would not be unintentional. Arya used the coin and the words, so we can expect somewhere out there, across the Narrow Sea, Jaqen is waiting and/or looking for her, willing to teach her how to kill and take names — and maybe new faces.
One popular (and very SPOILER-Y) fan theory has Jaqen appearing in Oldtown as a character from the books called the Alchemist, but that character has yet to cross paths with Arya. Our best bet is that Jaqen will be involved with Arya's training at the House of Black and White, the headquarters of the Faceless Men. In the books, she interacts primarily with "the kindly man," yet it would make sense, from the show's perspective, to combine this character with Jaqen, even if Jaqen's original face is only seen briefly.
And, hey, maybe Jaqen can head over to Oldtown sometime after that. After all, a man has got to have multiple interests.