Children of the Sea

Children of the Sea (海獣の子供, Kaijū no Kodomo) is a manga series written and illustrated by Daisuke Igarashi, and serialized in Shogakukan's monthly seinen manga magazine Ikki. Shogakukan has released five tankōbon volumes so far, between July 30, 2007 and July 30, 2012. The manga is licensed in North America by Viz Media.

Plot
One summer vacation, Ruka meets two boys, "Umi" and "Sora," whose upbringing contains strange and wonderful secrets. Drawn to their beautiful swimming, almost more like flying, Ruka and the adults who know them are intertwined in a complex mesh...

Meanwhile, an unexplained anomaly is occurring all over the world: fish are disappearing. Thus begins a marine adventure of boys and girls to captivate all the senses!