"[4] As a producer, Mukai helped the early careers of many prominent directors, including Hisayasu Satō and Academy-Award winner Yōjirō Takita.

[9][10] Wanting to direct, but lacking the educational requirements necessary to be hired as a director at a major studio,[8] in 1965, Mukai moved into the lucrative new pink film genre.

That year he founded Mukai Productions and, with financial backing from Nihon Cinema, directed his first pink feature, Flesh (肉, Niku), which was distributed by Kokuei.

[9][10][11] Though the film was a plotless series of scenes in the life of a prostitute, Mukai's technical skill impressed early pink audiences and critics, and he quickly became a major name in the genre.

[13] The Bite (1966) was another early Mukai film shown overseas, playing in the U.S. soon after its Japanese release, and in Britain, under the title Bait, in 1967.

[18] He worked with his wife,[2] actress Takako Uchida, in several of his early films such as Nightly Pleasure (Yoru No Yorokobi, 1967), Stories of Adultery (Aru Mittsu, 1967), and Spring of Ecstasy (Kokotsu No Izumi, 1968).

Stories of Adultery was a three-part omnibus film, with other two segments directed by Kōji Wakamatsu and Shin'ya Yamamoto (director).

Takako Uchida later starred in Nikkatsu's big-budget pre-Roman Porno venture into the pink arena, Story Of Heresy In Meiji Era (1968).

[29] As producer, Mukai had an influence on the careers of the "Four Heavenly Kings of Pink" or "Four Devils" (ピンク四天王, Pinku shitennō) group of directors who came to prominence in the 1980s.

Hisayasu Satō began working in the film industry through Shishi Productions in 1981, and had his directing debut there with Mad Love!

During the 1980s, when rape-themed films were popular, Mukai produced some of Nikkatsu's most extreme examples of the genre, including the Subway Serial Rape series (1985–1988).