God Killer

Until the movie’s final twist (which, frankly, everybody saw coming), Diana believes that Ares can be killed only with a special weapon made for this purpose alone. So she steals the Godkiller, the Lasso of Truth, and her new battle suit.

By the way, is that white cube in the armory a Mother Box?

It’s later revealed that the sword isn’t a god killer at all, although in the comics, Hephaestus (the god of fire and, of course, forge) creates a sword designated for the purpose of killing titans. Wonder Woman has nothing to do with this sword; instead, it’s entrusted to Deathstroke (who we’ll hopefully see in the DCEU in the next couple of years) to kill Lapetus, a Titan enemy of Olympus.