suiguutou (juuni kokuki)

Suiguutou (水禺刀 Water Monkey Sword; Sword of Suiguu) is a sword that can be wielded only by the rightful ruler of Kei. The sword is accompanied by the Hekisoujo, a miraculous gem possessing healing powers. The sword, along with its scabbard, and the gem are sacred treasures in the kingdom of Kei.

The Suiguutou was forged by Tatsu-Ou, a previous great ruler of Kei, from a water youma and it was originally known as Suikantou (水鑑刀, Water Mirror Sword). When Tatsu realized the sword's power could bewitch the wielder, he forged a scabbard to contain its magic. Because the scabbard was made from a long-tailed monkey youma, Aozaru, the sword was renamed Suiguutou to reflect its new nature. The sword and scabbard change form with each new master; the blade originally took the form of a long-handled scimitar and eventually becomes a long sword for Youko Nakajima.