Kusanagi

Kusanagi is a Noble Art used by Ouma Kurogane.

Description
Kusanagi is the Ultimate Technique of Ouma Kurogane, which is the Wind Element variant of Stella's Katharterio Salamandra where he imbues magic in Ryuuzume, amassing wind around its blade, devouring the atmosphere all around the immediate surrounding area; manifesting an enormous sword of storming slashing wind reaching 50 meters in height, which slices apart everything in its path. At first, Kusanagi was able to overpower even Katharterio Salamandra in his initial battle with Stella and turned the school buildings, practice areas, asphalt into rubble, but it was overpowered by the same technique in the 62nd Seven Stars Sword Art Festival after Stella discovered her true power.

During his fight against Abraham Carter, Ouma later revealed Kusanagi in its completed form, Kusanagi – Shin'uchi, which he couldn't use wielding his power, but did so using pseudo mana amassing from the natural wind; resulting in his Ryuuzume taking form as a blade of light slightly longer than his device. He then released his new technique, Ikki no Kaze, which killed Abraham in a single strike.

Techniques

 * Shin'uchi: This is the Kusanagi in its true form, which Ouma couldn't realize through using his own powers alone, where he continues compressing the enormous tornado several times over using the pseudo magic gathered from his natural element (i.e. wind); this creates a blade of light that is slightly longer than his Ryuuzume. The presence of Shin'uchi was powerful enough to frighten Abraham Carter, a Desperado who described the thin wind blade as having the power to twist the space of the world.
 * Ikki no Kaze: Ouma's strongest Noble Art surpassing Kusanagi, which can be used after Shin'uchi has been activated, where he slashes everything within 500 km of the trajectory where Ryuuzume is swung in a straight line and powerful enough to kill Abraham.

Weakness
Kusanagi's power depletes with each usage, although with the third usage, it was still strong enough to withstand Nene's Black Sword・Yatagarasu. It also requires some time to activate.

Trivia

 * Kusanagi is named after one of the Three Imperial Regalia of Japan, also known as Ame-no-Murakumo-no-Tsurugi and later Kusanagi no Tsurugi, which is explained to be able to manipulate wind.