Words of Radiance (The Stormlight Archive, #2)

by Brandon Sanderson

And the Blade itself . . . was it black? An inch or so of it had emerged from the sheath as it slid on the rocks. Szeth swore he could see a small trail of black smoke coming off the metal. Like Stormlight, only dark. Hello, a cheerful voice said in his mind. Would you like to destroy some evil today?

This was dope if you've read Warbreaker