Ama no Murakumo no Tsurugi (Sword of the Gathering Clouds of Heaven), also known as Kusanagi no Tsurugi (Grass-Cutting Sword), is a legendary black Japanese sword, and part of the Imperial Regalia of Japan. It was formerly the property of the former Heretic God Susanoo and considered a demigod.

Ama no Murakumo no Tsurugi is a demi-god of Steel and has shown the Authority of Wind control, and the ability to enhance the wielder to a point where they can surpass the abilities of a Great Knight. It can also possess its wielder when they are in the Netherworld. It's suggested that both of these require the power of Divine Possession to accomplish though.

Since its introduction, Ama no Murakumo has revealed the ability to adsorb Authorities, whether those of its wielder Godou, or those of an attacker, to provide power, and transform them into new abilities. After absorbing the power of wind from the Authority of Luo Hao, it granted Godou the power of shockwaves from his punches, when adsorbing lightning created from Godou's Authority, it developed immense magnetic powers, and other abilities.
(Source: Campione! Wikia)