Yuu Aku has been one of Japan's most prolific and commercially dominant lyricists since the late 1960s. Over 500 of his compositions charted on the Japanese Oricon, collectively selling more than 68 million copies between 1968 and 2007—a figure that placed him as the second best-selling lyricist in the country by 2015, behind only Yasushi Akimoto. During the 1970s alone, more than 20 songs he wrote hit #1, with seven singles crossing the million-copy threshold.

His four-decade run as a lyricist earned him five Japan Record Awards, and he proved equally skilled as a novelist, producing several acclaimed works. The Japanese government recognized his massive cultural impact in 1999 by awarding him the Purple Ribboned Medal of Honor.

Health struggles marked his later years. Aku was diagnosed with kidney cancer and underwent surgery on September 12, 2001, but kept working through chemotherapy. He died of ureteral cancer on August 1, 2007.