Hiroki is one of several Japanese film directors who got their start in the Japanese softcore pornographic film genre of "pink film". He said in an interview that in the late 1970s when he wanted to get into directing, he wrote a script for a "pink film" and brought it to the Ōkura Eiga studio but they told him he needed to start as an assistant director. At this time he met prolific "pink film" director Genji Nakamura and during the next three years, Hiroki worked as an assistant director, editor, and manager for Nakamura's company Yū Pro. Hiroki made his first film as a director with "Sexual Abuse! Exposed Woman" for Million Film in 1982. His debut met with poor reviews and was "terrible" according to Hiroki and he went back to being an assistant director for a time.