Rumiko Koyanagi debuted in 1971 with the single "Watashi no Jyokamachi" ("My Castle Town"), which reached the #1 position on the Oricon charts and sold nearly 2 million copies. She performed for the first time at the 22nd edition of Kōhaku Uta Gassen and eventually made 18 consecutive appearances on the show. She was promoted alongside Mari Amachi and Saori Minami, and they were dubbed the "San-Nin Musume" (Three young girls).
Before them, Hibari Misora, Chiemi Eri and Izumi Yukimura were promoted in the same fashion.
In 1973, Amachi, Koyanagi and Minami were followed by Momoe Yamaguchi, Junko Sakurada and Masako Mori, who were known as "Hana Number Chu 3 Trio" (The Trio of Third-Year Junior High School Students). Her second single, "O Matsuri no Yoru" ("Night of the Festival"), sold over 500,000 copies and reached the #2 position on the charts.
In April of 1972 the single "Seto no Hanayome" ("The Bride of Seto"), became her second #1 hit. The single went on to sell more than 800,000 copies.
The follow-up single, "Kyo no Niwaka Ame" ("Today"s Shower Rain"), became her third #1 hit.
Several hit singles were released throughout 1973, and in the winter of 1974 the single "Fuyu no Eki" ("The Winter Station"), would prove to be her 4th #1 single. Her last big hit was produced in 1983. "O Hisashi Burine" ("lieutenant"s Been a Long Time"), reached the #8 position on the Oricon chart list.
Apart from being a singer, Rumiko Koyanagi is also an actress.