Shinju (from the Japanese 真珠 meaning pearl) is a euphemism to refer to the binding of female breasts. It has been popularly claimed that "shinju" is an authentic Japanese term for a "bikini harness". However, no such tie called a "shinju" is found in historic or present kinbaku.
The basic or foundational kinbaku form of binding the arms and breasts is known as the Ushiro Takatekote; which is to bind the arms behind (ushiro) the back in a box arm position (takate kote). This basic box arm tie originally found in the samurai martial art of hojōjutsu (捕縄術) or Nawajutsu, (縄術) evolved into its erotic usage at the end of the 19th century and early 20th century, and is foundational to most other kinbaku ties.
Read more about this topic: Breast Bondage