was a Japanese lyricist, poet, and novelist.

He was famous for contributing lyrics to many recording artists since 1967. Mainly during the 1970s, more than 20 of them reached #1 on the Japanese Oricon chart, and 7 singles sold more than a million copies. Over 500 of his compositions which were released as singles have entered the Japanese record chart, and they sold in excess of 68 million copies from 1968 to 2007, making him the most commercially successful Japanese lyricist up to that point. As of 2015, total sales of the singles he has written exceed 68.3 million copies, making him the second best-selling lyricist in Japan behind only Yasushi Akimoto.

hroughout his 40-year career as a lyricist, Aku won the Japan Record Award five times. He was also acclaimed as a novelist, and produced several award-winning works. In 1999, Aku received the Purple Ribboned Medal of Honor from the Government of Japan, in honor of his long-term contributions to the Japanese entertainment industry