Heko obi (兵児帯)
The heko obi is a kind of men's obi (sash) used in wearing wafuku (Japanese traditional clothes). There two types as shown below.
At present, kaku-obi for males that is made of soft textile is sometimes called 'heko obi.'
This one was originally called 'sanjaku obi' (three-foot-long sash), but later it was confused with heko obi. Refer to the article of "Sanjaku obi."
This name derived from the fact that Satsuma heko (young people in Satsuma Province) used it in their daily lives. After the Meiji Restoration, it became popular with the customs of Satsuma were introduced in Tokyo.
It later became the one that is used not only by men but also by children for wearing yukata (Japanese summer kimono), and even women sometimes use it at present.
It is used regularly for everyday clothes because it doesn't put excessive burden on the body when fastened thanks to its soft textile and width. However, it is avoided for street clothes as its knot looks untidy and easy to get loose.
Bits of Knowledge
In some schools of battojutsu (an art of drawing a sword), a kind of Japanese military arts, people tie it on their practice wear for the purpose of wearing a practice sword.
It is said that during the Seian War, Saigo's army tied the heko obi on their western clothes to wear the Japanese swords.