Futago no Teikoku

The story takes place during the 2595th year of the Ko (Light) Era. Ko, the country of the rising sun, invaded several countries and war rages. Its territory does not stop growing and in heaven, the battleships are a legion. Gaw, a young immigrant boy, and Fa, a mysterious young girl, will find themselves embarking on this "war."

(Source: animeland.com)