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Cognomen Koichi (Koichi , コウイチ , 浩一 , among others...) , globally, is a common surname. The cognomen Koichi is characteristic of Japan, where it is quite a common surname, Taiwan, where it is quite a rare surname, and Singapore. In absolute terms, the name is most common in Eastern Asia, particularly Japan, China, and Taiwan. Much less frequently, Koichi is the forename as well as the last name.