Why are Japanese soldiers' underwear triangular white cloth, and so are Japanese women?

First of all, it is not a "triangle" of white cloth. Second, a rectangular white cloth.

A belt is sewn on one short side of a rectangular white cloth and tied around the waist. Rectangular white cloth is gathered from the waist, passed through the crotch, and then turned out from under the waist belt, unfolded and flattened to block the genitals.

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This kind of "Japanese-style crotch cloth" was originally worn by Japanese men, but now some Japanese women have begun to wear it because it is very comfortable. And some businesses, optimistic about this business opportunity, have also begun to produce "Japanese-style crotch cloth" for women.

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"Japanese crotch cloth", because the crotch is open, there is no sense of urgency to wear, and it doesn't need the right size like underwear. "Japanese crotch cloth" is not affected by height and thinness, and it is comfortable to wear, simple to make and saves cloth.

So the traditional Japanese underwear is such a "Japanese crotch cloth".