[1][2] She made her debut as a professional manga artist in 1968 with the short story "Paula no Namida" in the magazine Weekly Margaret.
[5] According to Mizuki Takahashi, Ōshima is considered the most influential artist of the Year 24 group because of her visual innovation in shōjo manga, especially in panel design around representing emotions in drawing.
Takahashi writes: "The panels are not sequential, which forces readers to look at the whole page in order to understand the atmosphere of a scene rather than just read ahead in the story.
"[6] Many of her stories are centered on girls' anxieties during adolescence, the difficulties of dealing with becoming an adult physically and emotionally and needing to suppress one's child self.
She received the 1978 Kodansha Manga Award for shōjo for The Star of Cottonland,[7] and the 2008 Tezuka Osamu Cultural Prize Short Story Award for "Cher Gou-Gou...mon petit chat, mon petit ami," a short story in the ongoing series Gū-gū Datte Neko de aru.