Known most commanly as The Sword Kusanagi is said to have been created at the dawn of Unknown. Its said to have carved the great mountain the temple of Mo'a Keet where it is kept in its sheath and on display.
Its said that a great mountain spirit inhabits the blade which possibly explains the weight of the blade and that when struck by the blade is to feel like a flying mmountain would have hit you.
Though no one is truly sure of the validity of these claims for the Spirit inhabiting the blade will only ever grant is power to the weilder when a worthy enemy is present. However there is no existing records of the blade ever being used either.