is a legendary Japanese sword and one of three Imperial Regalia of Japan. It was originally called , but its name was later changed to the more popular ("Grass-Cutting Sword"). In folklore, the sword represents the virtue of valor.
Legends
thumb|Susanoo slays the eight-headed beast Yamata-no-Orochi
thumb|Prince [[Yamato Takeru and his sword Kusanagi no Tsurugi]]
The history of the extends into legend. According to , the god Susanoo-no-Mikoto encountered a grieving family of kunitsukami ("gods of the land") headed by in Izumo Province. When Susanoo asked Ashinazuchi, he told him that his family was being terrorized by the fearsome Yamata no Orochi, an eight-headed serpent of Koshi, who had consumed seven of the family's eight daughters, and that the creature was coming for his final daughter, .
Susanoo investigated the creature and, after an abortive encounter, returned with a plan to defeat it. In return, he asked for Kushinada-hime's hand in marriage, which was agreed to. Transforming her temporarily into a comb (one interpreter reads this section as "using a comb he turns into [masquerades as] Kushinadahime") to have her company during battle, he detailed his plan into steps.
He instructed that eight vats of (rice wine) be prepared and put on individual platforms positioned behind a fence with eight gates. The monster took the bait and put one of its heads through each gate. With this distraction, Susanoo attacked and slew the beast with his sword, Worochi no Ara-masa, chopping off each head and then proceeded to do the same to the tails. A rite at Hinomisaki Shrine honors this delivery to this day. Although the also contains mythological stories that are not considered reliable history, it records some events that were contemporary or nearly contemporary to its writing, and these sections of the book are considered historical. In the , the Kusanagi was removed from the Imperial palace in 688, and moved to Atsuta Shrine after the sword was blamed for causing Emperor Tenmu to fall ill. Along with the jewel () and the mirror (), it is one of the three Imperial Regalia of Japan, the sword representing the virtue of valor.
thumb|Artist's impressions of the (unseen) Imperial Regalia of Japan
is allegedly kept at Atsuta Shrine but is not available for public display.<!--Another record claims that this priest died from the curse and the power of the sword, but this is most likely a story that was spread to emphasize its power.-->
In The Tale of the Heike, a collection of oral stories transcribed in 1371, the sword is lost at sea after the defeat of the Heike in the Battle of Dan-no-ura, a naval battle that ended in the defeat of the Heike clan forces and the child Emperor Antoku at the hands of Minamoto no Yoshitsune. In the tale, upon hearing of the Navy's defeat, the Emperor's grandmother, Taira no Tokiko, led the Emperor and his entourage to commit suicide by drowning in the waters of the strait, taking with her two of the three Imperial Regalia: the sacred jewel and the sword Kusanagi. The sacred mirror was recovered in extremis when one of the ladies-in-waiting was about to jump with it into the sea. Although the sacred jewel is said to have been found in its casket floating on the waves, was lost forever. Although written about historical events, The Tale of the Heike is a collection of epic poetry passed down orally and written down nearly 200 years after the actual events, so it has questionable reliability as a historical document.
Another story holds that the sword was reportedly stolen again in the sixth century by a monk from Silla. According to Shinsuke Takenaka of the Institute of Moralogy, a 12th-century replica preserved in the Imperial palace is the one used in coronation ceremonies, probably due to the fragility of the original sword.
Other emperors' swords
The sword is always hidden because of its divinity, and it is put in a box and put up by the chamberlain at the time of the enthronement ceremony. However, the Japanese sword held up by the emperor's chamberlain, which can be seen at various imperial ceremonies, is always close to the emperor as an amulet, and is called . has changed over time; at present, two made by swordsmiths Nagamitsu and Yukihira in the Kamakura period play the role. Apart from these swords, the Imperial Family owns many swords, which are managed by the Imperial Household Agency. For example, one of the , , is owned by the Imperial Family.
The sword of the Crown Prince of Japan
The Japanese crown prince has inherited two , or , and . While the sword is forbidden to be seen because of its divinity and is always kept in a box, the Crown Prince's sword is worn by the Crown Prince with the traditional costume at an official ceremony of the Imperial Household.
The sword is the most important sword owned by the Crown Prince, given by the Emperor as proof of the official Crown Prince after the ceremony of his inauguration. Its origin is that it was given by Emperor Uda when Emperor Daigo became Crown Prince in 893, and the present, the sword is the second generation, made in the late Heian period. The sword is a made by Yukihira, a swordsmith in the Kamakura period, and the Crown Prince inherits it from the Emperor before his inauguration ceremony and wears it in various Imperial events except for the festival.