Ruka meets two lads, "Umi" and "Sora," during his summer vacation, whose childhood has unusual and amazing mysteries. Ruka and the people who know her are entwined in a complicated mesh because they are drawn to their exquisite swimming, which is almost like flying... Meanwhile, a mysterious phenomenon is causing fish to disappear all across the planet. Thus starts a sea adventure for boys and girls that will fascinate all of the senses!