Zecchô no onna (1976)

In order to win a spy war between companies, a company develops a cyborg sex machine that has no female emotions whatsoever, to infiltrate a rival company with a woman and use her own body to steal information from the opposing company. The older sister, who was transformed into this corporate spy sex machine, dies mysteriously. It was because she fell in love with a man from the rival company, and for some reason, despite being a cyborg, she became a real woman in front of him at the end. Unaware of these circumstances, the younger sister volunteers to become the cyborg sex machine herself in order to find out the truth about her sister's death...