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.
Natsu-kun! Natsu-kun, what's wrong?!
!ناتسو-كن! ناتسو-كن، ما الأمر؟
Natsu! Natsu! Was ist los?!
¡Natsu! ¿Qué pasa, Natsu?
¡Natsu! ¿Qué pasa, Natsu?
Natsu ! Natsu ! Qu’y a-t-il ?
Natsu! Natsu, cos'è successo?
Natsu-kun! Natsu-kun, o que aconteceu?!
Нацу! Нацу, что случилось?