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.
Coastal towns close to the sea level were 
enveloped by the ocean.
البلدات السّاحليّة القريبة من مستوى
البحر مُطوَّقة بواسطة المُحيط
Die niedrig gelegenen Küstengebiete
Las zonas costeras de poca altitud
se hundieron por completo.
Las zonas costeras de poca altitud
se hundieron por completo.
a provoqué la submersion
des territoires de faible altitude.
Le zone costiere al livello del mare,
Cidades costeiras, que ficavam no nível
do mar, foram todas engolidas pela água.
низкие участки земли оказались
затоплены вместе с городами.
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