As night falls, she meets Umi, a strange boy raised by dugongs who dives and disappears into the murky waters of Tokyo Port.

Children of the Sea, written and illustrated by Daisuke Igarashi, was serialized in Shōgakukan's seinen magazine Monthly Ikki from December 24, 2005, to September 24, 2011.

[19] The film is directed by Ayumu Watanabe, with Kenichi Konishi as character designer, chief supervising animator and unit director and music by Joe Hisaishi.

[30] PopCultureShock's Sam Kusek comments on the interactions between the main characters, saying, "[Umi, Sora and Ruka] all share something in common, the fact that they are outsiders from the norm.

Umi and Sora are obviously outsiders due to their extreme circumstances, wearing large robes to cover a majority of their skin and having to constantly bathe in water.

"[31] Anime News Network's Carlo Santos commends the manga for its "subtle, seamless storytelling and first-class artistry combine to form a fascinating tale of the sea" but criticizes it for "mundane events and superfluous scenes sometimes slow down the plot".

He also commends on Igarashi's "earthy art, with its busy line work and crosshatching and unsophisticated figure drawing, grounds this series in reality, which makes the moments of enchantment all the more breathtaking."