Tsurugi (sword)

A or is a Japanese sword. The word is used in the West to refer to a specific type of Japanese straight, double-edged sword used in antiquity (as opposed to curved, single-edged swords such as the katana). In Japanese the term "tsurugi or ken, " is used as a term for all sorts of international long, double-edged swords.
History.
The term tsurugi (剣) designates a straight, double-edged, bladed weapon from Japan. The tsurugi were usually forged from the 5th century (Kofun period) to the 9th century (Heian period). It is a sword, which means that this weapon has two edges, one on each side of its blade, unlike the tachi, katana, wakizashi or odachi, which have only one cutting edge, on one of the two sides of the blade. From the 9th century, the development of the curved tachi began, from which the katana emerged. After the 10th century, it was occasionally dedicated to Shinto shrines and Buddhist temples.
Nowadays it is mainly associated with very remote historical times, as well as legends and mythology. There are some similarities with the Chinese Jian (called Chugokuken (中国剣) in Japanese), but the Jian has a different design with a wider shaped blade.
Kusanagi-no-Tsurugi.
The most famous example is the legendary sword "Kusanagi-no-Tsurugi" which is one of the Three Imperial Regalia of Japan.
Tsurugi-tachi.
The Tsurugi-tachi -剣太刀, a straight sword with only one side of the blade sharpened throughout, was similar to the Tsurugi or Ken . The other (back) side was only worked into a second cutting edge in the front part near the tip.