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 deal is to use this thing to snatch up 
the treasure in my grandma's house and split it.
الاتّفاق هو استخدام هذا الشّيء لسحب
الكنز من منزل جدّتي وتقاسمه
Und diese Frau da behauptet,
dass in ihrem Haus ein Schatz liegt,
Quiere que vayamos por su tesoro,
Quiere que vayamos a por su tesoro,
On a prévu d’utiliser ce sous-marin
Dovremmo recuperare
 il tesoro nascosto in casa sua
O trato é usar isso aqui para pegar o tesouro
na casa da minha vó e dividir entre nós.
В её доме осталось
что-то ценное,
เขาบอกให้ไปเอา...