Shikougan

The is a kettou jouken that serves as the fifth and final eye in Nox's forehead. The kanzen shikougan allows the user to fire a black beam of super-condensed Negative Tao that causes catastrophic damage to everything it touches, even evaporating the air it travels through.

The kanzen shikougan was originally a much larger construct, the shikougan, created by Nox that tracked and fired at his will.