Of course, such a wide obi requires its own accessories: depending on the node (musubi in Japanese), there are cords, pads and scarves made especially to support it... And there are hundreds of node variants, because the node always says something about its wearer: there are nodes for girls and for married women, nodes for maiko, for brides or for various events...
One of the most popular nodes is the chōchō-musubi ("butterfly knot") - in the photo. It's a beautiful version and it is also available ready-made - tsuke obi.
EXIF info:
Nikon D90
Lens: VR 18-55mm F/3.5-5.6G
Focal Length: 24mm
Aperture: F/4
Shutter Speed: 1/60s
ISO Sensitivity: ISO 400