The first-ever theatrical anime film, Chiikawa: The Secret of Mermaid Island, hit the big screen on July 24, 2026, becoming a massive box office smash! In just two weeks, it raked in an impressive 5 billion Japanese Yen.
Recently, the official team dropped an exclusive interview with original author Nagano, conducted before the movie's release. In this chat, Nagano dives deep into his involvement in the film's production, the secret origins of characters like "Siren" and "Shima Jiro," the casting choices for voice actors, and tons of other behind-the-scenes tidbits.
Nagano-sensei was completely hands-on throughout every stage of Chiikawa: The Secret of Mermaid Island's production, ensuring his beloved work was brought to life perfectly. Below, we've broken down the interview into a Q&A format:
※This interview was conducted before the movie's release.
On the Theatrical Film
Q: With the first Chiikawa theatrical film about to premiere this year, what are your immediate feelings?
Nagano: I'm definitely nervous about the movie hitting theaters, but also incredibly excited! If I could, I'd love to go watch it with everyone. This theatrical film was a journey of many firsts for me, a bit like fumbling in the dark. We even started with fundamental questions like, "Should we even make a movie?" and "Can we actually pull this off?"
It's what you might call a happy problem, but since we were going for it, I absolutely wanted to make it great. Throughout production, I constantly wrestled with "How can I make this even better?" From drawing the manga in 2023 to the movie's release, I felt like my own time was stuck in 2023, never moving forward. So for me, it wasn't until the movie premiered on July 24 that I finally felt like, "Ah, I've finally entered 2024."
Q: How did you communicate with the film production team? What specific requests did you make?
Nagano: First and foremost, my biggest concern was not to mess with the original image of each character. For example, in an early scene where Chiikawa and Hachiware are looking at a flyer, when Chiikawa reaches for it from the side, I didn't want it to look like he was "snatching the flyer away in a flash." Beyond that, I made many incredibly detailed requests regarding the artwork, especially for character expressions. Things like the angle of their eyebrows, how wide their mouths were open, and so on. We also had regular meetings, sometimes in person, and I even participated remotely during voice recording sessions.
As for the movie's content, we'd discuss together which manga scenes to cut and which parts to expand, gradually fine-tuning everything. For instance, Director Kei Oikawa eats candy incredibly fast, from popping it in his mouth to crunching it down. I always felt like he must have eaten (and crunched) a ton of candy. How do I know? Because during remote meetings, I'd occasionally hear a "crunch..." as he bit into one. But honestly, hearing that candy-crunching sound actually made me feel relaxed and motivated, thinking, "Let's push through for the movie's release!"
When I'm adapting manga into animation, I actually don't know how many minutes a particular section will end up being, or how much pause is needed for viewers to feel comfortable. But I often get the feeling that the director can already see how the time will flow once it's animated. Sometimes, when I wanted to cut parts that I thought were important, the director would stop me, saying, "It's better to keep this here." He truly understands the strengths of this work and its characters, and you can feel his deep respect for the original material. I believe Director Oikawa's gentle demeanor also brought that unique "Chiikawa feel" to this movie and tied the entire piece together beautifully.
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I made an incredible number of detailed requests to everyone involved, including Chief Animation Directors Tomoko Tsuji and Aoi Maekawa, and all the animators. I'm truly grateful that everyone still put in their absolute best effort to complete the work. As for producer Taro Imafuku, he actually wraps a fork – you know, a regular eating utensil – around his arm. I thought that was pretty cool! Handy for digging if you ever get into a tight spot, right? (laughs) I bet I gave him a pretty hard time with all my requests! But even so, he helped bring so many of my ideas to life, and I could really feel his serious and sincere dedication to this project.
Q: How deeply were you involved in the production of this theatrical film?
Nagano: I checked everything down to the most minute details, from the animation to the storyboards. I imagine that original creators who are simultaneously working on animated films and ongoing manga series must, at some point, step away from the production due to their own commitments.
In contrast, I was in a position where I could get really deeply involved, which actually made me wonder: "What's the right level of involvement here?" However, I didn't want to have any regrets, so I poured everything I had into it.
Regarding Voice Acting Roles
Q: How were the voice actors for Shimajiro, Siren, Kazuha, and Futaba chosen?
Nagano: When selecting voice actors, of course, I consider whether they match the character's image, but I also look into who the voice actor is as a person – for example, what kind of things they like, those kinds of details.
Siren
For Siren, I envisioned someone who could be both adorable and terrifying, and ideally, a fantastic singer. I felt that Minori Suzuki-san perfectly matched what I had in mind, so we brought her on board. Her vibrato during the singing audition was absolutely stunning – that was the deciding factor!
Kazuha and Futaba
Casting Kazuha and Futaba was the trickiest part, as so many talented voice actors auditioned with incredible enthusiasm. Kazuha and Futaba look almost identical, but they each have their own distinct personalities. Ultimately, we decided on Momoka Terasawa-san and Sayumi Suzushiro-san because they were excellent at capturing each character's individual personality, even without dialogue. My directions to them were:
"Kazuha should have a slightly spacey, air-headed feel, while Futaba should be more reliable and steady."
Shimajiro
For Shimajiro, Tsuguo Mogami-san's voice was, of course, a perfect fit for the character, but his X (formerly Twitter) handle, "Nihonshu Namejirō," also played a key role in the decision! I was so thrilled to hear Shimajiro speak exactly as I'd imagined, especially the underwater Shimajiro – absolutely brilliant.
As for the mermaids, Saeko Ohki-san, Ayaka Nanase-san, and Nozomi Nagumo-san were also carefully selected after much consideration. During the recording, Masaki Tsuchiya-san, our sound director who has worked with us for a long time on the TV series, clearly conveyed the nuances and subtle emotions we wanted to the voice actors.
About the Opening (OP) Video
Q: What was the core concept behind the original design for the opening (OP) video?
Nagano: Since the "Chiikawa" TV anime episodes are quite short, they don't have a traditional opening theme. So, my starting point was, "If Chiikawa *did* have an OP, this is exactly what I'd want it to feel like!"
Given this is a movie, I figured many viewers might be experiencing Chiikawa for the first time. So, I also wanted the OP to introduce the characters and the world of the series. I absolutely adore anime OPs, so getting to be involved in this one was a huge thrill!
Q: What are some of the unique highlights in this theatrical film that only animation can truly deliver?
Nagano: The absolutely stunning backgrounds, and how even non-speaking characters are always bustling in the background – especially Usagi – are definitely worth noting. Plus, those cinematic compositions and dramatic pauses that aren't in the original manga? Those are charms that only come alive through animation.
Right at the start of the film, that scene where Chiikawa, Hachiware, and Usagi interact around the log – that's where I really felt the cinematic magic. Seeing it animated for real was incredibly moving. We poured a ton of effort into Siren's singing sequence and Usagi's rap. Oh, and there are even some spots where the voice actors improvised lines, which I personally love!
And there's so much more to see! The battle scenes, in particular, are incredibly powerful – I think they'll give everyone a much clearer sense of Otter's true strength, something that's harder to fully convey in the manga. Pay close attention to how the characters' physical movements and inner emotions are perfectly synchronized with the music throughout the film. It's tough to put everything into words, but I'd be absolutely thrilled if everyone could experience this movie firsthand in theaters!
About the Characters
Q: How did you come up with Siren and Shimajiro?
Nagano: I wanted to create a character that was both big and adorable, so Siren was designed with "That Kid" (Anoko)'s appearance as a target. In the early sketch phase, her look wasn't fully set, so I initially placed "That Kid" in the role of the siren. Her head is modeled after an Inuhariko (a traditional dog-shaped papier-mâché doll), while her lower body is red, giving off a goldfish-like vibe.
As for Shimajiro, he evolved into his current form after I pondered, "How can I make him look truly dependable?"
Q: What changed in the "Siren Arc" compared to your initial concept when you started drawing it?
Nagano: In the initial sketches, Ichiyo and Niyo actually had faces and dialogue, but I later felt like "they were talking too much." Plus, I personally prefer characters without dialogue, so I ultimately changed them to a form where their faces and lines aren't directly seen or heard by the audience.
Shimajiro wasn't originally planned to appear, but I wanted a dependable companion, so I ultimately decided to introduce him. Actually, there was a character called "Sake Manju" who was supposed to appear – he looked very much like a chestnut manju and was envisioned as something like the island's village chief. However, that plan was later scrapped, so I think it worked out really well that we ended up adding a new character named Shimajiro instead.
On the Music
Q: What were your requests for the film's music?
NAGANO: For the music, I really wanted to bring in Shugo Tokumaru, who we've collaborated with on the TV anime series. Ultimately, Mr. Tokumaru and Chikara Kamimizutaru were in charge of the score. My main request was to establish an "island theme song" first, and then have different arrangements of it play at various points throughout the film. You'll hear the "Lots of yummy stalls ♬" melody pop up in different places, and I'd be thrilled if everyone notices it!
The musical-like atmosphere when Siren makes her entrance is also fantastic, especially that cool shot where the camera slowly approaches from behind Chiikawa and Hachiware just before Siren reveals herself—you absolutely have to hear it! While I recommend every single BGM track, I'm particularly fond of "Futari no Himitsu" and "Shukkou no Asa."
Q: What are your thoughts on the completed opening and ending themes?
NAGANO: For both the opening (OP) and ending (ED) themes, we first created the lyrics, and then Mr. Tokumaru composed the music based on them. He truly crafted both songs into magnificent pieces. I was incredibly moved the first time I heard the demo versions. It was also wonderful to witness the songs gradually come to life as new arrangements were continuously added.
The OP is truly amazing; it perfectly captures both the powerful intro before the movie title appears and the overall vibe of the "Chiikawa" world. I also adore the ED, which has a lovely Southern island feel to it. That final segment that plays after the song ends really gives you that "the movie is truly over" sensation.
Finally
Q: Did you ever think, "One day, I want to make a 'Chiikawa' movie"?
NAGANO: Honestly, I was already completely blown away just by "Chiikawa" becoming a TV anime, so I never really thought, "I want to make a movie next!" For me, "Chiikawa" and "movies" weren't really connected concepts to begin with.
It took me about two or three years to truly grasp that "Chiikawa" was actually airing as a TV anime. So, with this movie, I imagine it'll probably take another couple of years before it truly sinks in that "the movie has actually premiered."
Q: How do you hope audiences will enjoy the film?
NAGANO: I hope everyone can simply enjoy the cute and fun sides of the characters and have a great time with the movie. If kids watch it, I hope that when they grow up, they'll remember, "Oh, I saw a movie like that once." I want this film to leave a little memory in the back of their minds, something that might become a foundation for them if they ever want to create something in the future. After all, the animated films I watched as a child have always stayed deeply rooted in my own heart.
Q: Will there be another "Chiikawa" movie in the future?
NAGANO: For this film, I approached it with the mindset of "this is the first and the last," pouring everything I had into it. But, if the opportunity ever truly arises again... I'd love to make a movie starring Shimajiro! The plot? "The story of Shimajiro and Ode's epic showdown."
via： 『映画ちいかわ 人魚の島のひみつ