アイよりアオい海の果て

In the future, nations and civilizations have disappeared due to rising sea levels caused by tectonic movements and global warming. The survivors lacked technique and talent, but they were able to restore an ancient battleship and attach a spare hydrogen engine to it. Then, a long long time passed, and all land was inundated by the sea, and humans barely survived aboard the self-navigating self-repairing ship.

Ao is a boy who lived in the town aboard the ship. He helps out his parents with plowing the fields and fixing the fishing gear. There is no entertainment aside from visiting the floating market once a month and gazing at the passing ancient flotsam and pondering what they were once used for. It was a relatively depressing life akin to living in a closed society.