One of the 24-Gumi (Magnificent 49ers), the group of female manga artists that pioneered the shoujo demographic.

She made her debut in 1968 with Paula's Tears in Weekly Margaret. Her works have a very surreal feeling. Ooshima is said to be a very eccentric person.

Kutsuwada Chie is a fan of hers.

She received the 1978 Kodansha Manga Award for shōjo for The Star of Cottonland, and the 2008 Tezuka Osamu Cultural Prize Short Story Award for Gū-gū datte Neko de aru. She is credited with popularizing the kemonomimi (catgirl) character type through her creation of Chibi-neko from The Star of Cottonland.

She approaches profound and disturbing issues in eccentric ways, fooling the reader into thinking she's reading a cute, nonsensical farce, then leaving her in tears.

In 1997, she was found to have ovarian cancer, had an operation and has recovered. She wrote about it in her later works.