Taiji ga mitsuryosuru toki (1966) by Koji Wakamatsu
aka: The embryo hunts in secret
Yuka (Miharu Shima) dives all excited into a long desired adventure with her boss (Hatsuo Yamatani). Unaware of his second “second” thoughts, she has soon to discover, that rather than enjoying a romantic love affair, she is going to be taught a very painfull lesson.