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.
Are you sure she won't just 
throw you into the ocean
هل أنت متأكّد من أنّها لن ترميك في المُحيط
Was, wenn sie sich nach
dem Fund des Schatzes bedankt,
¿No te tirará al mar
en cuanto tengan el tesoro?
¿No te tirará al mar
en cuanto tengáis el tesoro?
Elle ne risque pas
de te jeter à la mer
Non è che, appena trovato il tesoro,
Será que, assim que encontrarem
o tesouro, ela não vai agradecer
А вдруг найдёшь это сокровище,
она скажет спасибо