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.
One day, he entered the ship’s engine area, which the adults had told him absolutely not to enter. There was a picture from long ago, showing girls in colourful clothes dancing at a school in front of a large crowd of happy children. This was a ‘culture’ which has long since been lost. Moreover, he found a girl sleeping within a capsule. She was wearing the same clothes as those shown in the picture.
The capsule opened when he touched it, as if he had authenticated something. The girl appeared to have lost her memories, aside from one thing: that she is an idol. An idol’s job is to sing and dance, and to spread happiness to everyone. Ao and the self-proclaimed idol Ai set out to revive the idol culture in this small world floating on the sea.