Frozen yogurt is incredibly difficult to come by in Japan. Sure, you can find yogurt everywhere, and throw it in the freezer if you feel so inclined (or an ice cream maker). Yet the widespread prevalence of soft cream all over this country surprises me that frozen yogurt has not yet become as ubiquitous. There are a few shops in Tokyo, in Osaka, and some of those large, urban areas, but if you aren't in a large metropolis, you're generally out of luck.
Unless you're in Shizuoka prefecture.
