Hakunagi, literally; Spirit Cutter, is Seireitou Hyuga's Shadow Blade that he made while training with Zukia Tojiro. He recently finished the blade because he has been customizing it, but rarly uses it on account of his default weapon being KyuubiTaishou. It like the Kusanagi Sword is unbreakable and can cut through any substance. Like Samehada, it can cut through chakra. Due to certain Cyber Crystals in the blade, it can absorb chakra as well. It also has shown to be able to trasform into a Naginata. It is able to conduct Seireitou's Elemental Chakra and chakra from KyuubiTaishou, allowing him to make jutsu unique to the sword and himself. Also the sword can only be used by him and if taken it can teleport back to him.
This blade is later given to his son, Suzaku Hyuga