Chiikawa and Hachiware are relaxing in the square when Usagi turns up with a flyer stuck to its face. Hachiware peels it off and finds an invitation to a special island. Won over by what the flyer promises, the group decides to go on an island retreat, and Rakko, who finds the flyer suspicious, boards the same boat. The islanders give them a warm welcome. Then the group hears that a giant siren living on the island has been carrying the islanders off one after another, and they are drawn into a plan to defeat it.
The film is based on a long story Nagano posted on X, known as the Siren arc. The official site introduces it as one of the most popular episodes in the series, a story that trended on social media more with each new installment. Nagano drew the manga in 2023 and wrote both the original story and the screenplay for the film. This is the first time Chiikawa has been made into a film.
Animation is by Cypic, and the director is Kei Oikawa. Toho released the film in Japan on 24 July 2026. In a notice dated 21 September, the official site said the film had passed 15.84 billion yen in its first 59 days and ranked first among 2026 releases at the box office, according to Kogyo Tsushinsha.
In Korea, Daewon Media imported the film and released it on 30 September. According to Daewon Media, cumulative admissions passed one million on the afternoon of 9 October, ten days after opening. Among animated films released in Korea this year, only Toy Story 5 and The Super Mario Galaxy Movie have drawn more viewers.
In the official interview, Nagano said the siren was meant to be a big, cute character. Its head is modeled on an inu-hariko, a papier-mache dog figure, and its red lower half is drawn like a goldfish. The TV anime has no opening sequence because each episode is so short, so for the film Nagano personally worked out the concept for the opening. Expecting some viewers to be seeing Chiikawa for the first time, Nagano built it to introduce the characters and their world. Nagano also said that because the fight scenes were made more dynamic, they should get across how strong Rakko is, something the manga rarely manages to show.
