She is best known for her appearances in Nikkatsu's Roman Porno films with an S&M theme during the 1970s. Her debut was in the 1967 film Special. She took her screen name "Tani" from the novelist Jun'ichirō Tanizaki and "Naomi" from the central character in his important early work A Fool's Love. "Tani," or "valley," is also a Japanese slang word for the cleavage between the breasts. Consequently, Ms. Tani may have had a variety of puns in mind when she later opened a restaurant calling it the "Ohtani" (Big Breasts or Big Tani).

Tani's first experience with an S&M film was in one episode of the omnibus film Memoirs Of A Modern Female Doctor (1967), and her first full-fledged S&M leading role was in director Masanao Sakao's Female Bodies in a Brutal Scenario (1967), in which she plays a prostitute who repeatedly escapes from, and then captured and tortured by the yakuza. Tani would play similar roles for Sakao in other films such as Virgins With Bad Reputations, also made in 1967.

Known for her remarkable dedication to her work, Tani would perform even the most extreme of S&M scenes without complaint. During the twelve years she worked as an actress, she never went to the beach or allowed herself to get a suntan, feeling that it was important to keep her skin very white, so that it could be seen turning red during some of the scenes involving such things as whippings or melting candle wax tortures. Tani wrote in 1998 "The woman's naked body must not only be seen as a sensual object, but must also be able to express emotion; so, I did my best to keep Naomi Tani's body as close as possible to perfect condition."