Chiikawa The Movie: The Secret of Mermaid Island has become a huge box office success in Japan, earning 6.77 billion yen (around $43 million/£34 million) in just 17 days and making it the fourth highest-grossing film in the country this year. The success is notable because the source material, while marketed as a cute "comedy" and "slice of life" story, is also a "dark fantasy" that has been read as a critique of the gig economy, featuring life-or-death missions, deaths of adorable characters and body horror. The film adapts one of the franchise's darkest storylines, reportedly reducing some children in the audience to tears.

Chiikawa began as a web manga on Twitter by the artist Nagano before being collected into eight volumes that have sold more than 3.6 million copies, and it spawned a 367-episode anime running since 2022. The film, animated by studio Cypic, opened to over $6.2 million on its first day (the seventh-biggest opening in Japanese box office history) and has now grossed more than $280 million worldwide. Reactions on social media to its horror elements have stirred curiosity in regions where the film has not yet been released, though the series currently lacks a full official English-language release, having previously streamed on HIDIVE and now only partially available via Amasian.