The Bank of Japan Silver-convertible Note with a Blank backs (裏白札)
In 1972, during the Showa period, the Japanese government issued bills with blank backs. Many people withdrew money from the bank all at once, and the bank needed a large number of bills in a short period. Therefore, they issued them without printing the reverse side to cut costs. This is also called Urajiro-Satsu (裏白札).