In the near future, much of the world has been forgotten at the bottom of the ocean due to rising sea levels. Natsuki Ikaruga, who lives in a small town surrounded and stranded by the sea, is invited by a mysterious woman, Catherine, to search for a treasure in his grandmother's house who was a marine geologist. One day, he dives to the bottom of the ocean in a submarine and encounters a mysterious capsule with a girl sleeping inside. The girl was a humanoid so sophisticated that she could be mistaken for a human.
The expansion of seawater 
due to global warming.
توسُّع ماء البحر بسبب الاحتباس الحراريّ
War es aufgeheiztes Meerwasser,
das sich ausgedehnt hatte?
Expansión del mar
por el calentamiento global,
Expansión del mar
por el calentamiento global,
Dilatation thermique
de l’eau de mer,
Ci sono numerose teorie a riguardo,
A elevação do nível do mar
pelo aquecimento global...
Может, дело в глобальном потеплении,