Set in the context of the world in 2040, the entire earth had fallen into drought and only Japan was able to survive after it by inventing a method of cell compression. It's a world where everything has been made smaller: The diminished world. It is the underwater city called JURA.
Two kids that live in the new version of the world start to connect through a transient period and remind themselves of how pretty the old Earth is and so as their childhood. As they grow up, they go on a journey in an unfamiliar world where survival situations happen every day.