Night Life was a 1982 erotic graphic adventure game by Kōei, released for the PC-8801 computer. It was the first commercial erotic computer game, featuring sexually explicit images and a precursor to the modern bishōjo game genre.
Night Life was marketed as an aid for the sex life of couples. It included such features as a schedule to determine a woman's period, and a catalog of possible sexual positions, with artwork consisting of black-and-white outlines.
Source: Wikipedia, "Night Life (video game)", available under the CC-BY-SA License.