Kusanagi (草薙) or Ame no Murakumo is Kazuki's sword that he obtained in Volume 9. It is also one of the Three Regalia that can only be found in Mt. Fuji's Haunted Ground. If someone possesses the three of them, that person becomes Japan's King. It was wielded by many swordsmen, including Kazuki's mother Hibiki.
Out of the Three Regalia, Kusanagi represents Japan's King offensive power, as it is said that Kusanagi can cut through anything, including magical phenomena.
Kusanagi has the appearance of a double-edged ancient sword. What makes it unique in the form of the hilt.
Kusanagi was a sword that the Shinto God Susanoo encountered when he was fighting against Yamata no Orochi. By unknown reasons, it was later passed through generations and was found in Mt. Fuji's Haunted Ground. Kazuki's mother found the sword and engaged Loki in a battle, resulting in a mutual defeat. Before her death, Hibiki sealed her spirit and the sword in the third level of Mt. Fuji's Sea of Trees by using her remaining life force and Lemegeton's power.
During the Treasure Hunting of the Haunted Ground in Volume 8, Kazuki's mother reacted to his presence and lent him some of Kusanagi's power to defeat Ilyaelia. After Kazuki's battle, she encourages her son to reach the summit of the mountain and claim the sword.
The Kusanagi is the ultimate sword in Japan. The person that is able to wield the Kusanagi can cut through large quantities of magic power and magical phenomenons. Like many Sacred Treasures, Kusanagi can pass its knowledge of its power to the user, but it is up to that person to master its abilities to the fullest.
- Battou Kaikon ― Kusanagi no Tsurugi: One of the Incantations used to unleash Kusanagi's offensive power. After chanting, the user can cut through magical phenomena and make them disappear.
- Battou Kaikon ― Tsumugari no Tachi: Another one Kusanagi's incantations. The user can slash a magic attack, absorb and compress the magic power to give Kusanagi the attributes of the magic and increase its offensive power.
- Battou Kaikon ― Shirakumo no Yoroi: An incantation that creates white clouds that then cover 4-5 allies and hardens creating white cloud armor that protects from fire, electricity, and physical attacks.
- Battou Kaikon ― Kushihebi no Tachi: Kusanagi becomes able to twist and stretch like a snake making its trajectory hard to read or predict.
- Battou Kaikon ― Shiratori no Misasagi: An incantation that creates a pair of white wings with soft plumage on the back of the user that allows them to fly through the air at high speeds.