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 fact that there's some treasure deep down 
in your granny's house is the absolute truth!
حقيقة وجود كنز في الأعماق
!في بيت جدّتك مُطلَقة
Ich weiß mit hundertprozentiger Sicherheit,
dass im Haus deiner Oma ein Schatz schlummert!
Está confirmado que hay un tesoro
en la casa de tu abuela.
Está confirmado que hay un tesoro
en casa de tu abuela.
Il y a un trésor chez ta grand-mère,
je le sais de source archi sûre !
In casa di tua nonna
è sepolto un tesoro
Tem sim um tesouro escondido
na casa da sua vó. Sem erro!
В доме твоей бабушки есть сокровище —
это точная информация!
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