Chiikawa the Movie: The Secret of the Mermaid Island

Once upon a time, Siren, a legendary creature whose song could work magic for the plants, came to an island with three mermaids. The islanders offered tributes of food to the Siren, and she rewarded them with harvests by singing to crops help them grow. One day, the Siren was playing with the mermaids and unknowingly destroyed a boat with two islanders, Hitoha and Futaba on board. They had previously know that anyone who ate a mermaid could gain eternal life.

Futaba was badly injured, leading Hitoha to kill a mermaid and cook it at home. Futaba was revived and healed by gaining eternal life after being fed a piece of mermaid by Hitoha, but they were horrified at the thought of immortality with no one else around and made Hitoha eat it as well. Hitoha and Futaba then discovered a battery slot on their bottoms. They quickly understood the meaning of "eternal life" – when their "life" ran out, they could be "revived" by replacing the battery. They promised to keep the secret forever.

Meanwhile, furious at the death of one of her mermaids, Siren abducted and ate the islanders until the culprit was found. None of the other islanders knew about the disappearance of the mermaid or the reason for Siren's aggression. As a result, the islanders forbade anyone from contacting Siren and invited visitors from outside to help suppress Siren. In response, Siren also attacked visitors who tried to suppress her.

The film begins with Usagi, one of Chiikawa's friends, receiving an invitation letter to the island offers promising rewards including meals. Many of the residents (recurrent characters of the series: Chiikawa, Hachiware, Usagi, Momonga, Furuhonya, and Rakko) then visit the island following the invitation. There, they enjoy the meals and celebrate. At night, Chiikawa, Hachiware and Usagi accidentally enter Siren's cave and learn about her what happened to them.

The next day, an islander announces the mission to suppress Siren and find missing villagers, while most promises are lies, scaring off visitors and leaving only Chiikawa and friends to defend. Siren then attacks the village and visitors, and Chiikawa is the only one who manages to escape. Chiikawa encounters Shimajirō, the owner of a restaurant in a remote area who makes clam soup and spicy curry rice. Chiikawa, with Shimajirō's help, frees all the captives held by Siren, including two of the villagers who had previously disappeared. Shimajirō holds off the Siren, allowing everyone to escape. Convinced Siren would attack again, Rakko tries to conjure up a plan. Chiikawa, who ate Shimajirō's curry rice, suggests making a very spicy curry rice to disable Siren's singing attack.

Siren appears the next day. Chiikawa and friends force the spicy curry rice they prepared into her mouth, but Siren enjoys the spiciness and unaffected by the curry. Then, Shimajirō protects others from Siren's attack and offers the Carolina Reaper, saying that it was the only pepper that would be overly spicy for her. After forcing the Carolina Reaper-laced curry into her mouth, Siren begins writhing in pain and hits Hachiware and Chiikawa with her tail. Futaba protects them and hit by the her, knocking out their battery cover. Noticing the battery cover, Siren acknowledges Hachiware's plea to stop attacking the islanders and retreats to the waters to ease the spiciness in her mouth.

While nursing Futaba in their home, Chiikawa witnesses Hitoha replacing Futaba's battery and combined with the knowledge of the mermaid scale in their home before, Chiikawa figures out Hitoha and Futaba were the ones who killed and ate the mermaid. At the celebration of the Siren's defeat, Chiikawa tries to talk to Hitoha and Futaba, but ultimately stays silent and returns to enjoying the party. The next day, Chiikawa and friends depart the island with gifts and cheers from the islanders. On the ship, Usagi sees the mermaid scale from Hitoha's home in Chiikawa's pochette. As the ship moves, the scale drifts back towards the island by wind. Seeing the scale flying off, Chiikawa starts chatting with friends.

In the post-credits scene, Hitoha and Futaba are revealed to have fled the island; they arrive on a new island and decide to reside in a cave. In the nearby ocean, Siren and her two remaining mermaids swim towards the island, closing in on the two immortal fugitives.

The film is based on the manga's "Siren Arc" (Japanese: セイレーン編) or "Island Arc", which was serialised from March to November 2023. The screenplay was written by Nagano, credited as the original story. Under Nagano's supervision, Kei Oikawa of Cygames Pictures was selected as the director. Production companies QTORY, Cypic, Fuji Animation Studio and Toho are the film's distributors.^[1][4]

The opening and ending theme songs, respectively titled "Kutsuzure" (くつずれ, lit. "Shoe Sore"), performed by Makoto Tanaka,^[4] "Tsukue Sasuru" (机さする, lit. "Desk Rubbing"), performed by Haruka Aoki, are both written by Nagano.^[5]

Siren's visual design is based on an inu hariko (papier-mâché dog) for the upper body and a goldfish for the lower body.^[6] The inu hariko is a talisman believed to have originated in Nagoya's Atsuta Shrine, and is used to pray for fertility and safe childbirth, while the goldfish is a speciality product of Yatomi, Aichi Prefecture; This work features other elements evocative of Aichi, such as soy sauce and miso; the local preference for strongly flavoured dishes; curry reminiscent of CoCo Ichibanya, a company based in Aichi; Japanese manila clams, a seafood product for which Aichi boasts the highest catch volume in Japan; Kasugai City in Aichi is said to be the birthplace of Yao Bikuni [jp], who ate mermaid meat; and Shiruko Sand [jp] used as bait to lure out the mermaid.

"AA battery" in Japanese is usually shortened as tansan (単三), which is a homophone of the short name for carbonated beverages tansan (炭酸); It is also a soundalike of minor third (短三度, Tan-Sando), the music interval sung by a slain mermaid.^[7]

The promotional song for the food stall that the islanders had been singing ever since the Siren arrived contains an acrostic message "We apologize—please help us." (おわびじゃ たすけて, Owabija. Tasukete).

The list of Okinawa topics performed by Shisa: Kōrēgusu is a kind of chili sauce common in Okinawa made by steeping chili peppers in awamori (the distilled spirit); Yushi-Dohu is hand-made Shima tofu; 'Yuntaku' means chatting with chill in Ryukyuan languages; The song Shisa sang is UNION(ja)'s commercial jingle, a supermarket chain that operates only on Okinawa Island.

It was released in Japanese theatres by Toho on 24 July 2026.^[8] The film was subsequently released in Taiwan, Hong Kong, and Southeast Asia with the former two receiving Mandarin and Cantonese dubs alongside the original Japanese soundtrack, respectively.^[9][10][11]

Its film content ratings in airing locations are:

Since its release on 24 July 2026, the film has been the most-watched movie in its opening week in Japan, with 1,508,500 tickets sold and around 2.24 billion yen in revenue.^[4][20] As of 6 September, the film has grossed 14.6 billion yen from 10.1 million tickets sold.^[3] Internationally, the film has grossed NT$147 million in Taiwan and HK$24 million in Hong Kong as of 6 September.^[21][22]

The film involves bleak subjects such as revenge, murder, guilt and eternal torment despite the series' light-hearted nature. Many social media users described the film as a "horror movie" despite its perception as a family film.^{[20][23][24][25]} Audience reactions were noticing gloom, such as a comparison of a wake, some young children were seen leaving in tears.^[20][24]

Some social media users compared the film to the works of Kanae Minato, a Japanese crime fiction writer best known for Confessions. Noticing the comparisons, Minato watched the film and praised it as "interesting", adding that "a bad ending is more about reflecting on morality and what is right than enjoying others' sufferings". She also commended Nagano's decision to avoid showing Hiroba and Futaba's faces, calling it "kind".^[26][27][28] Patrick St. Michel of The Japan Times compared the film to Crime and Punishment by Fyodor Dostoevsky.^[24] A review in The Yomiuri Shimbun praised the film as "approachable", with main characters who are easy to empathise with and a good artwork that can present the original manga world.^[29]