This girl is Kanako, the main character's girlfriend, whom he has gotten pregnant. The first time they had sex, they totally forgot about contraceptives, and she got knocked up.

Kanako is not bothered by this turn of events, and says she wants to have the baby. Though the main character refuses to let Kanako face the hardships of parenthood alone and agrees to take responsibility, Kanako's mother, Kikuna, steps in and forces the two of them to begin living together as husband and wife starting right now!

While according to their parents, it'd have been better if the two should have flirted and built up their relationship a bit more before this, with Kanako pregnant as she is, it's too late now. Of course, this arrangement does nothing for the MC's burning libido, which is not being fulfilled!

To help, Kanako agrees to do what she can for him, and the two begin blazing new trails in pregnancy-safe eroticism. Furthermore, Kikuna also joins in, stating she'll work as a substitute for Kanako! Where will this strange course of events lead them?