Because the units of Japanese yen and RMB are both circles (yuan/yuan/yen).

The origin of the Japanese yen "Y": The British and Americans at the end of the Bakumatsu period called _ yen instead of the Japanese Roman character en. In order to cater to the habit of two lines in the US dollar, two horizontal lines were added to the initial letter Y. Source of RMB "Y": The RMB symbol takes the first letter Y of the pinyin of the RMB unit "yuan" Yuán, plus two horizontal lines to form ￥. The Japanese pronunciation is en. The symbol consists of the Latin letter "Y" and two parallel horizontal lines. The reason for using the Latin letter "Y" is because the English spellings of "yuan" and "yen" both start with "Y". If these two currencies are to appear at the same time, add the word CNY before the RMB symbol "￥", or add the word JPY before the Japanese yen ￥.