Keys of Oblivion is a signature weapon used by Herrscher of Sentience, the weapon itself is not a single weapon but a pack of 4 different weapons: Short sword, spear, chain blade and "Sword in Shealth".
Trivia
It is the first weapon in the game to have different equipment display when comparing icon to full weapon image.
死穴 is a technique used in 武俠 to kill using seemingly less than lethal force targeted at specific areas of the body. It is also used to incapacitate or sometimes cause immediate or even delayed death to an opponent.