Mantis Female Secretary (1984)

Takashi Shirakawa, the president of Tozai Corporation, is an adopted son-in-law. His wife, Reiko, is sickly and their married life is indifferent. His secretary, Mitsuko Mizukami, who has been having a physical relationship with the president, is an adulterous woman who plans to seduce the president into letting her wife commit suicide so that he can get his wife Meigi's fortune.