I see every darkness and misery in all the Realms. Every bloody horror of this war. Every damned one of Malekith's crimes. As the wielder of Bitterblade and the new guardian of the Black Bifrost...I see more Dark Elves dying this day. 
History
A cursed sword created to serve as a dark counterpart to Hofund, the Bitterblade was bequeathed by Malekith to Bitterhand, marking him as the Guardian of the Black Bifrost.[1]
After Bitterhand was killed by Freyja, she took the weapon for herself to become "Dark Freyja" - augmenting her already immense divine power to the extent she could fight off a seemingly endless horde of dark elves, and giving her all-sight for all things dark and evil.[2]