Deep Throat in Tokyo (1975)

Original title: 東京ディープスロート夫人

Kumi Taguchi is a model who leaves her boxer boyfriend after he sustains an injury. She meets and quickly marries Hideo, the heir to a corporate empire. Hideo's father, Takehiko, lusts after Kumi. Takehiko sends his son away, ostensibly on a business trip, but actually so that he can be murdered by Takehiko's henchmen. Takehiko seduces Kumi, but is frustrated when she refuses to perform oral sex on him. Angered, Takehiko forces Kumi to undergo surgery in which her clitoris is transferred to her throat, thereby requiring that she engage in oral sex in order to have an orgasm. Hideo, the supposedly murdered son, returns having paid off his assassins. Hideo shoots and kills his father, but Kumi grabs the gun and kills Hideo so that she can inherit the family's fortune