The kogarasu-zukuri (pronounced "ko-gah-rah-soo zoo-koo-ree") is a rare and old design. The back of the blade sports an edge halfway, while the remaining half of the blade sports a wide spine. The center of the blade is fullered. The Kogarasu-maru or "Little Crow" is more of a polearm design. There are three surviving kogarasu-styled blades in existence today, one in the National Tokyo Museum.

One cannot help but wonder why the design was not continued. Perhaps the abrupt change in the spine from thick to thin creates a great stress point in the final heat treatment. Another possibility is that the Japanese favored single-edge swordsmanship. It may have been that the design in itself is complicated and significantly more difficult to produce than a standard shinogi zukuri style blade. The Kogarasu-maru was a tachi blade, and a surviving original from the early Heian period measures 62.8 cm in blade length. It is said that this is an 8th-9th century sword but the deisgn in itself is more befitting a halberd. The temper line is a straight sugaha style. The tip is a moroha design (kissaki-moroha where kissaki means "tip")

INFORMATION from "THE JAPANESE SWORD" by Kanzan Sato
ILLUSTRATION BY ADRIAN KO