This blade is important because it is not only fully intact, but also signed and dated on the outside of the blade, a combination known as a kaikudashimei. Tsugunao is considered to be the foremost Aoe smith of the Nambokucho period. This is one of the longest of his remaining daito. The longest is a 90.9cm. katana belonging to the Tokugawa Reimeikai Foundation.
The early period Aoe tradition, or school (Ko Aoe-den) was founded by Yasutsugu at the beginning of the 12th century and continued until the middle of the 13th century. The blades were of a pronounced koshi-zori; the most outstanding characteristic of the Aoe blades was the pattern of the steel itself, normally a mixture of small wood grain and burl, a pattern known as chirimen, resembling crepe silk. The Aoe kaji also produced a second, coarse surface said to resemble the skin of catfish and known as namazu-hada. The tempering pattern was typically straight, frequently with 'legs' and sometimes with some small clove or irregular patterns.
The middle period Aoe (Chu-Aoe) tradition lasted until about 1370 and was influenced by the nearby Katayama Ichimonji. The shape changed very little, but the surface showed more of a fine-grained wood pattern intermixed with sumi-hada, as in this example. The tempering pattern remained straight, but became more Ichimonji in style with the introduction of sharply slanting 'legs' and irregular clove patterns.