Kogarasu Maru/Origin

The Kogarasu Maru "Little Crow" is the most famous of the known Kogarasu Zukuri blades and is currently in the Japanese Imperial Collection. The tang of the Kogarasu Maru is not signed but the blade is believed to have been made during the either the early Heian period or late Nara period, by the sword smith Amakuni, who is said to have created the first curved Japanese sword and is believed to have lived during this period. Two other Kogarasu Zukuri blades exist from this era, but many other blades of this type have been created throughout Japanese history.

The Kogarasu Maru is believed by some to have been a cut down naginata or yari blade that was fashioned into a tachi, as its shape is similar to that of some polearms. Nevertheless no evidence of "suriage" (shortening) is found on any of the three extant examples from this time period.