Shinju (from the Japanese meaning pearl) is a torture technique applied to women in the Japanese bondage technique. Humiliation with mild or severe pain is caused by tying different kinds of ropes and knots round women's breasts. Breasts can be tied to look like grapefruits or they can be pressed flat. This technique may cause serious damage if the blood flow to breasts is interrupted for too long.
However, classic shinju is not related to torture. It is done by encircling the torso with rope, both above and below the breasts, sometimes with cinches between the arms and the body. Then take the primary rope from the centre of the back over one shoulder, entwining both torso loops, and then back over the other shoulder, tying or weaving the rope to secure at the back.
The key to shinju is that the rope is, when done properly, never tied, it is weaved and intertwined. The same strand of rope is used to "tie" the submissive up. When done correcting tension can be applied to the end of the rope that then pulls tension throughout the weave.
Like this for example . . .

One strand of rope is used to intertwine the entire body, keeping the person restrained, but not in pain. If the proper amount of tension is applied.
Notice how the rope starts at the torso, and wraps over the shoulders, so that it can then be pulled to wrap the hands (at the wrists) behind the back, and then at the buttocks to then secure the legs (many times in several places) at the ankles and sometimes the thighs or knees.

It is, as many things, something that must be learned and practiced to be able to do it properly and without harm to the person being bound.
A practice that has been around for centuries, and obviously is something desired within some humans souls. If it weren't for supply and demand, things wouldn't be around.
For some instructions and help with rope bondage twines and knots check out the following link
http/www.nawashi.com/tutor/sjm.htmlEternally . . . Her_Slave