It is a band clasp for wearing a kimono.
It is a convenient dressing item that can be firmly fixed without tying the obi.
At the end of winding the obi two times, use this tool to pinch all the obi and stop the button on the bottom.
There is a recess on the top where you can put the obi pillow, so you can fix it firmly by putting the obi pillow on it.
You can wear it without worrying about losing your clothes even with the violent movements of Awa Odori.