What is the box worn with an obi?

The box worn with an obi is called an "obiage." It is a decorative piece of fabric placed underneath the obi, often serving both a functional and aesthetic purpose. The obiage helps to hold the obi in place and can also add a splash of color or pattern to the overall kimono ensemble. Typically made from silk or another fine material, it is tied in a knot at the back or left hanging, depending on the style.