Tapioca starch (polvilho) in Japan: what it's called and where to buy it
Tapioca starch is タピオカ粉. It isn't on every supermarket shelf, but baking shops and import shops sell it.
Look for this on the label
タピオカ粉
tapioka ko
タピオカでん粉
tapioka denpun
片栗粉
katakuriko · potato starch