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.
There are a number of theories like 
these, but nothing's been confirmed.
،هناك عددٌ من النّظريّات المُشابهة
لكن لم يتمّ تأكيد أي واحدة منها
Theorien gab es viele,
doch niemand kannte den genauen Grund.
Hay varias teorías,
pero ninguna confirmada.
Hay varias teorías,
pero ninguna confirmada.
Plusieurs théories existent,
mais l’incertitude perdure.
e i movimenti della crosta terrestre,
Existem muitas teorias a respeito,
mas nenhuma foi confirmada ainda.
Есть несколько теорий,
но ни одна не подтверждена.
มีทฤษฎีมากมาย