Kansen 2 - Inzai Toshi

One day a couple of students wake up inside a wrecked school bus, then they discover that their city is in ruins and some people wanders with some weird looks. They found that there is a virus that makes people have insane sexual desire and they wont think on nothing else, and that virus is transmitted via sex so they must save their companions before they fall for that virus or even them will lose their will.