On earth's last day the survivor is a hikkikomori?

The country called Yukifune is now in an age of air travel, and a group called Saratros exists during these times. Armed with blimps and gliders, what is the Sarastros' true nature, and what is its purpose?
Meanwhile, the army's watch for the Saratros takes a mysterious turn... and soon, Koto, the girl with the golden hand, will deal with the world as she makes her way out of the huge fighting stage!