Her work in Nikkatsu's Roman Porno genre included eight entries in the Apartment Wife series from 1972 until 1974.
Among the highlights of her early career were starring roles in Tanaka's Showa Trilogy (A Woman Called Sada Abe (1975), Watcher in the Attic (1976), and Beauty's Exotic Dance: Torture!
An exceptionally good actress for the genre, she was nominated for a Japanese Academy Award for best new actress in her roles in Kihachi Okamoto's film Dynamite Bang Bang and Hideo Gosha's Bandit vs. Samurai Squad (both 1978).
From the 1980s, she began working more in mainstream films, including two award-winning films for Mitsuo Yanagimachi: Fire Festival (Himatsuri) (1985) and About Love, Tokyo (Ai ni tsuite, Tokyo) (1992).
Commenting on his work with Miyashita, director Noboru Tanaka later said, "I liked her natural manner.