Yosuzume

Yosuzume (夜雀,Night Sparrow) is the name of Kōzuki's sword. It is a black katana with a blackened silver blade sporting a black hilt. At the base of the blade is a red crystal with reaches to the center of the blade. Engraved on the hilt are symbols, which he states are used to call his summons. This is done by flowing chakra into the hilt, the chakras then flows into the crystal. The at the instant of a slash a create is summoned, which are often used as a follow up to an attack. In addition his is able to flow his natures into it, much like the summoning. This is done from the hilt into the crystal then into the blade. Oddly, Kōzuki refers to Yosuzume as a "She".