[1][2] Kasagi frequently sang songs composed by Ryōichi Hattori, including 1947's "Tokyo Boogie-Woogie", which remains her best-known work.

[1] Yoshinori Gyobe, a professor at Nihon University, said that with Hattori's bright boogie rhythms and Kasagi's lively singing of melodies that did not exist in Japan, the duo changed the image of Japanese music.

[1][3] According to Michael Furmanovsky of The Japan Times, their 1939 song "Rappa to Musume" was the first recording in Japanese music history to feature scat singing.

[1] However, during World War II, the Japanese government was cracking-down on Western music, and the vigorously dancing Kasagi received directives from authorities to stand still, no farther than 1 meter from the microphone.

[1][3] The couple had talked of marriage and Kasagi retiring, but she decided to raise their child as a single mother and continue her career.

[5] Kasagi appeared in Akira Kurosawa's 1948 film Drunken Angel, performing the song "Jungle Boogie", the lyrics to which were written by the director.