Tachi, Amakuni and Kogarasu Maru

The tachi (太刀^?) is one type of traditionally made Japanese swords (nihonto)^[1][2] worn by the samurai class of feudal Japan. The tachi style of swords preceded the development of the katana.

Amakuni (天國^?) is the legendary swordsmith who created the first single-edged longsword (tachi) with curvature along the edge in the Yamato Province around 700 AD. He was the head of a group of swordsmiths employed by the Emperor of Japan to make weapons for his warriors. His son, Amakura, was the successor to his work. Although there are almost no modern examples of signed works by Amakuni, legend has it that the double-edged katana, Kogarasu Maru, was forged by this man. The true author of this work is not known, though the work bears similarities to works of the various Yamato schools so it is thought to be an early example of work from this province.

The Kogarasu Maru (小烏丸), or "Little Crow," is a unique Japanese tachi sword rumored to have been created by legendary Japanese smith Amakuni during 8th century CE.

The Kogarasu Maru was designed with a curved double-edged blade approximately 62.8 cm long. One edge of the blade is shaped in normal tachi fashion, but unlike the tachi, the tip is symmetrical and both edges of the blade are sharp, similar to a European sword or a Japanese yari spear, except for about 20 cm of the trailing or concave edge nearest the hilt, which is rounded. 

The Kogarasu Maru "Little Crow" is the most famous of the known Kogarasu Zukuri blades and is currently in the Japanese Imperial Collection.