A formal attire in summer for ladies of a high-grade warrior in or before the Shokuho era (Oda-Toyotomi era) - the Edo period, which will be described in detail later.
Koshimaki is also another name of belts which are wrapped around the lower part of publications such as books and mooks (magazines with the characteristics of books), indicating their titles, prices, advertising copies and so on.
In the Sengoku period (period of warring states in Japan), uchigi (ordinary kimono) which had ever been a formal attire for ladies of a high-grade warrior went out of fashion, and then ladies of a warrior got to put on the uchikake (long outer robe) over to show up dignity and protect against coldness. But because it was very hot in summertime, they came to tie the uchikake around with a cord at the height of a waist, and to take off the upper half of it. This is the origin of koshimaki. What has been drawn in the "Portrait of Lady Oichi" which is kept in Jimyo-in Temple, a tatchu (sub-temple in the site of main temple) of Koya-san, is a typical koshimaki in this period.
In the Edo period, Edo bakufu (Japanese feudal government headed by a shogun) laid down the regulations on costumes of the women in O-oku (the inner halls of Edo-jo Castle where the wife of the Shogun and her servants reside), and the other Daimyo families (feudal lord families) came to follow this convention, too. According to the regulations, "koshimaki" should be as follows: the term of wearing it was May 5 - September 8 (in old lunar calendar); the background color was black; when one wore it, she hung the sode (the sleeves of the kimono) with a special obi (kimono sash) called "sageobi."
In the end of the Edo period, the koshimaki came to be used only in the special ceremonies, and in or after the Meiji period, it went out of use completely.