In a nondescript time, in a nondescript world, a new resource has changed the course of human development. It's a type of crystal/gemstone/mineral/shiny thing, that when processed by those with magical ability, can be made to do most anything; from powering machinery/appliances to creating powerful weapons. This becomes the centrepiece of the global industry, and soon everything from stoves to battleships is powered by it.
The world's governments have now merged and hold an enforced monopoly on the mining and selling of the crystals. They have since become corrupt, and use less than honest methods of distributing and profiting from them. To combat this, a thriving black market was established by pirates seeking to get to crystal deposits before the gov't and sell it themselves. Some of them act like "Robin Hoods", while some only want power and money. They use crystal-powered flying ships to travel the world looking for more crystal deposits to mine. It's a cutthroat world, however, and pirates frequently attack each other to steal claims and increase their prestige. Clashes between pirates and government ships are also common.
Nozomi is a young girl seeking to join this world, and slowly builds up a pirate crew of her own. Her aims are pure, she wants to carve out her own niche and sell crystals at a decent price and help foster a better and more fair society (but mostly get really, really rich). Along the way, she attracts the ire of her future arch-enemy Kaguya and her crew of powerful dark-magic users who are out to conquer the black market and the world. In her adventures, Nozomi and her crew run into Kaguya constantly, and also meet a ton of vastly different crews from around the world, some who are just as evil, but also some of the good ones. She will inevitably run afoul of the government as well, and confront them and their privateers.
It's obviously a very infantile story, but the point is for it all to be very lighthearted and fun with hopefully some good action and maybe some romance thrown in. It's meant to be something that a kid or an adult can read and get into. And of course, it'd have plenty of moé fanservice, as all the characters are female.