The new cast members include (left to right in image above):
- min Tanaka as Jim, a former friend of Anglade and a marine biologist who now takes care of Umi and Sora
- Seishū Uragami as Sora
- Win Morisaki as Anglade, a genius marine biologist who pursues the mystery surrounding Umi and Sora
Airu Kubozuka was initially announced to play Sora. However, he dropped out of the role since he had trouble with his voice changing due to puberty.
When Ruka was younger, she saw a ghost in the water at the aquarium where her dad works. Now she feels drawn toward the aquarium and the two mysterious boys she meets there, Umi and Sora. They were raised by dugongs and hear the same strange calls from the sea as she does.
Ruka’s dad and the other adults who work at the aquarium are only distantly aware of what the children are experiencing as they get caught up in the mystery of the worldwide disappearance of the oceans’ fish.
The film also stars, from left to right in the image below, Sumiko Fuji as Dede (a mysterious figure who watches over Umi and Sora), Goro Inagaki as Masaaki Azumi (Ruka’s father who works at an aquarium), Yuu Aoi as Kanako Azumi (Ruka’s mother, whose relationship with both Riku and Masaaki is strained), and Toru Watanabe as Sensei (the coach in charge of Ruka’s hand-ball team).
Joe Hisaishi of Studio Ghibli fame is composing the music for the film. Ayumu Watanabe (Space Brothers, After the Rain) is directing, and Kenichi Konishi (Tokyo Godfathers, The Tale of the Princess Kaguya) is the animation director and character designer.
Igarashi launched the manga in Shogakukan‘s IKKI magazine in 2007, and ended it in 2011. Shogakukan published five compiled book volumes for the manga, and Viz Media published all five volumes in English. The manga earned nominations and awards of excellence from the 38th Japan Cartoonist Awards, the American Library Association’s Young Adult Library Services Association, the School Library Journal, and the 13th Japan Media Arts Festival Awards.