Yu Oikawa, who has been shut up in his house, is certain to die as a virgin at the age of 21. This is because the whole world has become a place filled with zombies... One day, a survivor visits Yu's house. The woman, who calls herself Sunny, injects Yu with a vaccine that may save the world from the zombies... but as a result, Yu gains the ability to turn zombies back into humans by having sex...?