In 1960 (at the age of 13), she was introduced to Nobuko Yoshiya,[2] a commercially successful novelist who specialized in serialized romance novels for teenage girls and is known to be the pioneer of Japanese lesbian literature.

[2] On September 1, 1923, the Great Kanto earthquake strikes and Mizushima is affected in her region.

Her pen name was created upon the release of The Song of the Fallen Leaves (Ogasawara, 1924), a film for which she wrote the script, in order to avoid expulsion from Japan Women's University, where viewing films (and therefore partaking in any production) was prohibited.

[3] She received on screen credit for this film, making her the first Japanese woman to have been recognized as a screenwriter.

In 1928, she wrote the screenplay for Sora No Kanata (Beyond the Sky), based on the novel by Nobuko Yoshiya.