In a future Japan, a meteorite strike has brought an end to the human race. The helicopter in which she was riding with her family crashes, saving the life of a young girl named Kaina, who is now a one-armed woman and leads a fulfilling life deep in the mountains with her benefactor, a volcano named Aramagi Volcano. One day, however, an encounter with an "arm" brought by a man who visited the volcano greatly distorts and accelerates Kaina's destiny.