Many PC-98 games interest me, some bore me, but it's a rare few that manage to really make me laugh at their own perversity. SakuSaku Daigoutou Returns was one of them, and this one doesn't quite manage to top that game, but it's close. This game originally came out for the PC-8801 which is pretty obvious due to the primative graphics. However, what it lacks in graphics it makes up for in subject matter.
You wander around the city visiting sex stores and accosting women on the street. The R key brings up the "Rape" command. If it has a pair of X chromosomes, you can assault it on a public street. The best moment was when I attempted to rape an ATM, at which point a cop attacked me and killed me.
The title is a play on words regarding the title of a rather famous sci-fi novel. The company that published this generally doesn't do hentai games. I don't believe KOEI is the actual developer, the PC-88 site I linked seems to mention some other company.