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.

(Source: Campione! Wiki)