Kogarasumaru Amakuni

Kogarasumaru Amakuni (小烏丸天国 Kogarasumaru Amakuni) is a black katana from the Kusakabe Seven Swords that Misuzu Kusakabe used most often. It is sealed in her index finger's nail.

Although it has no stated abilities, the Kogarasumaru is shown as if it was emitting some sort of power and before Misuzu's battle against Misao Kusakabe, Misuzu said that its power was nearly depleted and it needed some time to regain power.

In the anime, Misuzu would use this weapon most whenever she gave Raikiri to Kakeru Satsuki. She would use it in conjunction with magic and other swords such as Kannagiri and Kashagiri. She had fought both Invidia and Acedia on separate occasions using this sword.

Overview
Being 62.7cm in length, the sword is curved at its center, but is completely straight after that curve. Upon mentioning this blade, it should be noted of its interesting design as if it was a mixture between the continental double-edged "sword" and the Japanese katana. As well as that, this katana also is a mixture between the double-edged sword and the single edged katana. The straight half of the katana, as mentioned above, is crafted like a double-edged sword, while the curved half is crafted like a single edged katana.

The Kogarasumaru has a story behind it that it was said to have been given by a crow that had a wingspan greater than 8 shaku (one shaku is 30.3cm). The name Kogarasumaru refers to the distinct crafting of the sword, while Amakuni is said to be the name of the swordsmith who forged the katana (some speculate that he might be a fictional character and such a swordsmith never existed).

Trivia

 * Curiously enough, this katana was said to be created during the Heian era, which was around the same time the Japanese katana achieved its curved design.
 * This katana exists in reality as the prized sword of the Heike family, and as the possession of the Meiji era emperor.