In the distant future, the Earth had undergone a dramatic and extremely devastating change in its overall planetary climate, due to the Sun's abnormal activity. As a result, the entire Earth suffered a planet-wide Ice Age, forcing mankind to make a decision; either remain and freeze, or leave the planet to seek a new home among the stars.
Apparently the bulk of the human race chose the latter, though there were some survivors who did not wish to abandon the planet. This would eventually cause the humans to splinter into three sub-species; one Earth-bound and those who would eventually form the Galactic Alliance of Humankind and the Hideauze.
Throughout the centuries, the existence of the Earth would eventually be a long-forgotten memory to the people of the Galactic Alliance and seen as only a myth. However, with their new planet of Avalon under threat by the alien race known as the Hideauze, one soldier named Ledo and his Machine Caliber Chamber are swept into a time-distortion wormhole and into a 6-month-long hibernation state. When they finally awaken, they find themselves on a different world. The world was earth, and they meet with the descendants of the ones who stayed behind.
The surface of the planet is now mostly covered with water. When the glaciers finally melted, most of the land was submerged, and even the concept of 'land' is unknown to the current inhabitants.The natural wildlife is mostly aquatic or amphibious.
Floating across the vast oceans are 'galaxy currents' which happen to be large swarms of organisms called lightbugs. These lightbugs store electricity, (most likely by ionizing saltwater), in which the people of Earth use to power their ships. Since these currents do not last forever, every scavenger fleet must keep moving in order to find new ones, once the previous one runs out. The amount of electrical power that is generated by these currents is unknown, but can cause bolts of lightning to shoot upwards toward the sky.
Despite being completely covered in water, the people of Earth obtain fresh water for drinking and washing from rain, and anxiously collect it using whatever means at their disposal.or by refining the salt water
Though it is not mentioned how humans managed to survive the planetary Ice Age, it is apparent that they had adapted to this new environment. However, much of the pre-Ice Age technology and knowledge is now at the bottom of the oceans. As a result, the Earth dwellers have regressed to a level of technology equivalent to that of pre-World War II. Short-wave radios are considered as the most advanced form of technology. Maps of the world are now based on underwater landmarks and ocean currents. Weaponry is limited to old-style gunpowder projectiles. Flight is based on gliding with very little in terms of propulsion. The usage of rocketry is nearly unheard of and is mostly due to finding some examples by chance. Resources and raw materials are brought up from the ocean floor by salvage teams, which include old sunken battleships and other vessels, creating what are called scavenger fleets.
Humankind now live on these resurrected hulks, and use whatever technology is found on them, thereby becoming floating colonies. Several ships can choose to link together, thereby forming larger communities and sharing resources. There are examples of terrestrial plants and animals, as well as agricultural ships that raise them, most likely through the generations. Food is obtained either by fishing or by raising livestock and farming. Power is primarily harvested by following the galaxy currents, making the human race on Earth as nomadic. Machines called Yunboros are developed to perform heavy duties and for defense. However, there are marauding bands or pirates that prey on other colonies. It is because of these pirates that many colony ships agree to band together as a form of mutual defense. Gargantia is an example of one of the largest of these united colonies.
Due to the fact that cooperation is essential for survival, the taking of human life unnecessarily is seen as repugnant by most, though there those who do not share these views, such as the pirates. Shows of force is seen as methods of negotiation and the side with the bigger force is usually the victor, but there are those who ignore these unspoken rules. With the appearance of Chamber, the balance is drastically tipped toward the Gargantia with the pirates and other colonies scrambling to even the odds.
Knowledge about past civilizations before the planetary Ice Age has been mostly lost, and what is retained is based on hearsay or myths. Existing records and literature about the past are scarce. Even the story of the Great Departure into space is treated as nothing more than a fairy tale before the arrival of Ledo and Chamber. Concepts such as computers, artificial intelligence and space travel are unknown or treated as fantasy. The gap in technology is so huge that a single Common Machine Caliber is considered the most powerful weapon on Earth.
Several Treasures exist under the sea. Most are resources required to build new ships. However it is possible to come across rarer treasures such as records of the lost age, or fallen space debris. The rarest treasures however, is protected by Whale Squids and is the location of their nests. It can be assumed one would need an army of Yunboro to even stand a tiny chance of getting treasure. There is another way though, as former ensign Ledo has learned.
Pinion got weaponry treasures or tech most of it was thought lost at first except blueprints he got striker and the box which had beam weapons inside it the box which lobster mech was carrying turns out all of the beam weapons it somehow manage to survive Gargantia shoot and was later retrieved and and all the tech or treasures where reverse engineered by gargantia. Except the blueprints given by striker which they currently working on reverse engineering and building.