Two Japanese officials signed the Japanese Instrument of Surrender: Mamoru Shigemitsu and Yoshijirō Umezu.
Shigemitsu signed for the Emperor and the Japanese government, while Umezu signed for the Imperial General Headquarters. Their separate roles reflected the civilian and military authorities whose surrender commitments had to be represented in the document.
The Japanese delegation actually contained eleven officials, which is why the number is often misremembered. Only Shigemitsu and Umezu placed signatures on the instrument. The other nine delegates included officials from the army, navy, and Foreign Ministry, and their names had been submitted to the Allies in advance.
The Allied side had multiple signatories. After MacArthur signed for the Allied powers, representatives of eight additional Allied nations signed, including Chester Nimitz for the United States. The ceremony therefore involved many officials, but only two Japanese representatives signed for Japan.