Starving Anonymous Re:Velation

It's a day like any other, and high school students Ie and Kazu are on the bus home from school when, suddenly, it floods with a mysterious gas. The pair pass out and wake up to find themselves aboard a truck packed full of human bodies. They're surrounded by rows of frozen corpses... and a staff of living human beings sawing them into pieces. Where are they... and how can they escape from this nightmare? (Source: Kodansha USA) *Note: Includes two extra chapters.*