While there, she meets a mysterious pair of brothers, named Umi ("sea") and Sora ("sky"), who her father tells her were "raised by dugongs," and are being observed for their aquatic abilities.

[17] On April 8, 2019, the first trailer of the film was revealed on social media, previewing a minute or so of footage and the voice of Mana Ashida as protagonist Ruka Azumi.

The short-term exhibition also displays the original manuscript of the Children of the Sea comic and special unused images which were cut out from the movie.

Following an awards-qualifying run in 2019, a US theatrical release was planned for April 2020,[27] but was postponed due to the closure of theaters during the COVID-19 pandemic.

[35] The original musical score of the film is composed by Joe Hisaishi, a long-time collaborator of Studio Ghibli.

This film, together with Ni no Kuni, released two months later, mark Hisaishi's first two scores for animated feature films since 2013's The Tale of the Princess Kaguya, directed by Isao Takahata,[36] and the first non-interactive animated productions not produced by Studio Ghibli with music by Hisaishi since the release of Venus Wars in 1989.

The critics consensus is: "An animated adventure perhaps best appreciated as a visual experience, Children of the Sea is strikingly lovely if less than satisfying on a narrative level.

Kim Morrissy gave the film a C+ rating, with praise for the visuals and criticism of the "obtuse" nature of the plot.

"[42] In his review for Variety, critic Peter Debruge praised the film for its "splendid attention to detail and seemingly boundless imagination," for composer Joe Hisaishi's "lovely" score, and for director Ayumu Watanabe's "stunning adaptation" and exploration of the "age-old tension between those who recognize a rare and fragile being that they wish to protect and the callous impulse to experiment.