The main character Toshio is an ordinary student who likes games. On the first day of summer vacation, two beautiful girls from the future appear in front of Toshio's eyes. The names of the two are Tomoyo and Yuki. "We have received your sperm from the future three hundred years later." Toshio who is surprised and surprised by too loud talk. On Earth after 300 years, human genes were completely analyzed. And genes that make excellent brains, genes with high physical ability, genes of longevity, genes of beautiful forms ... all the parents replaced the genes of the child they were born to make excellent children. However, artificial gene manipulation that spans generations has caused serious problems. Children born from parents with similar genes had a high probability of having birth defects, and the birth rate itself dropped sharply. Finally, the men are gone, and the few remaining frozen stored spermatozoa are also low. Therefore, a project to collect as many sperm as possible was started back to the time before genetic manipulation was performed.