Progenitor — a series by haramiru

Impregnation / rapid pregnancy / birth fetish series. A dying man is reincarnated by aliens, with the mission of spreading the next stage of human evolution. His pheromones make him irresistible, and nearly every woman he inseminates becomes pregnant with eggs, which she then delivers in short order. Then other women are irresistibly drawn to insert those eggs into their own vaginas, where each egg develops into a normal (although slightly evolved) human fetus.