The weapon looks like it can be split into two functioning weapons, a detail more or less confirmed by Game of Thrones weapons master Tommy Dunne in an interview with Vanity Fair when he referred to a "showstopper" weapon. "There is one creation in Season 8 that is absolutely phenomenal," he said in the interview. "It was great to make, great to design in that it was able to be reverse-engineered and made into two different items."
Right after Arya reveals the schematic to him, Gendry asks why she "needs" a weapon like this and she doesn't really respond. It's a good question, one of the many that the short scene inspires. It looks like a weapon best used for fending off White Walkers, like the Game of Thrones equivalent of Darth Maul's double-sided lightsaber, and we know Arya has been trained with a staff. (RIP to the Waif.) Could Arya Stark be the character who kills the Night King? Or will this new piece of equipment be used to cross a name off her list? Or maybe she's just going into doomsday-prepper mode and is looking for something to add to her arsenal?
We do know that Arya's larger journey, her continued evolution from a brave child into a brilliant warrior, will be one of the main plot threads going forward into the series finale. (She also wasn't the only character to receive a weapon last night: Bronn was presented with a crossbow to kill Tyrion Lannister with.) After all, the opening images of "Winterfell," which tracked a young boy as he ran through the crowd to catch a glimpse of Daenerys and Jon Snow's arrival on horseback, were a direct callback to the pilot, as creators David Benioff and D.B. Weiss explained in the behind-the-scenes making-of after the episode. She's no longer an observer of history; she's making it herself. All she needs is the proper tool -- and now she's got it.