This is long staple 18 meter Egyptian cotton thread is made by Olympus, who have been making sashiko products for decades in Japan. The thread is a little thicker than the regular sashiko thread, so the stitches will be even plumper. This is what you want for the Kogin style stitching, and some of us like this look for regular Sashiko stitching, and for Boro stitching.
I've photographed the threads on navy fabric to let you see it against that color, and included a picture of a collection of the kogin threads so that you can compare the colors.
If you want a similar thread in a larger skein (145 meters) search 'Coron sashiko thread' by clicking on the little magnifying glass top right corner of this page.