Unlocked through a dlc code.
Obtained after defeating Ghorn.
|“|| A weapon of incredible power, forgotten to the eons. Formerly brandished by an ancient lich warlord whose reign of conquest faded into dust. Locked deep in the tombs below the Dead Plains, thought never to resurface. The only remnant of his tale is inscribed in runes on the weapon's blades.|
— In-Game Description, Darksiders II