Godkiller

From the various comic book iterations of Wonder Woman, we know that Diana strays away and doesn't care what destiny has in store for her. The same goes for the movie, as Godkiller, the weapon left by Zeus, ends up in Diana's possession (not the same sword used in Batman v Superman: Dawn of Justice).

The weapon is the only one capable of killing Ares, and can be wielded only by the fiercest of Amazons. So is it the DCEU’s Mjolnir? Does that mean that true power (and, thus, the ability to kill Ares) resides in the one who wields the sword, rather than in the sword itself? We don’t know.

However, we can assume that Diana takes the Godkiller only after she’s completed her training. Most likely, she knows that Ares is behind the War, and that only this sword can stop him. We’re certain only that surprises will happen, and we believe that the Godkiller is not just an enchanted sword, but one whose true power can be revealed only by Diana.