Sixth Sense is an essence gem which grants a large bonus to Intimidation while imposing a moderate penalty to the other two conversation skills. It is a counterpart to Divine Radiance and Strong Arm, which provide equivalent boosts for Charm and Intimidation, respectively.
It can be obtained in the Necropolis, being found in chest within the Tomb of the Masses.
In-game description: "Never has a man or woman had greater fortune than a lowly farmer named Jun Bin. His mother gave him an amulet on the day of his birth, and he only removed it at the end of his life. He never knew misfortune and, indeed, could not understand it when others tried to explain it to him. He was kind of distracted, neither loved nor hated. The evils and ills of the world just never touched him, as if he was always in exactly the right place to avoid danger and harm. Such goes against the order of the Heavens, though, and the one time he removed the amulet, the Heavens struck him down."