By 2010, all men had vanished after a dramatic environmental shift and an unknown contaminant swept through the world, causing the population to drop to its lowest point in history. Only women remained, huddling in isolated pockets of a planet largely reclaimed by nature. Some accepted their inevitable extinction and lived carefree lives, while others sought to preserve their species through scientific efforts. The society is marked by constant conflict over differing principles and policies. The story centers on the heart of Tokyo, one of the few habitable areas left for them, where tensions rise around a specimen of ICE that might hold the key to saving humanity.