Based on the manga by Koume Keito.

In this alternate reality sex is not a reserved theme—it is not even a discrete thing. This is due to the existence of female and male pollinic humanoids, who travel just like pollen via the air and when they find a receptive human they start their process of fertilization—or at least that’s what they intend to do. It’s just normal to see them everywhere and all the time during their season, and there are only few ways to avoid them, so almost everyone is caught up in the pollinic humanoids’ mating allergy.