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Kenshi Yonezu recently sat down with Billboard Japan to discuss his new single “IRIS OUT / JANE DOE.” “IRIS OUT” was written as the theme song for CHAINSAW MAN – THE MOVIE: REZE ARC, while “JANE DOE” serves as its ending theme. “IRIS OUT” sets impulsive vocals and comical lyrics against a swinging groove, while “JANE DOE,” a duet with Hikaru Utada, depicts a world that is both beautiful and dark. Together, they form a striking contrast.

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On the Billboard Japan charts, “IRIS OUT” hit the 100 million–stream milestone four weeks after its debut — the fastest ever in the chart’s history. Meanwhile, on the U.S. Billboard Global 200 that covers more than 200 countries and regions worldwide, the track achieved the highest ranking ever for a Japanese-language song, hitting No. 5 on the chart dated Oct. 4. In step with the movie, the single is currently making waves both at home and abroad.

In this latest interview, Yonezu shared the thoughts that shaped this release, as well as the changes in his day-to-day life after completing his world tour.

First off, tell us about how you’ve been doing. Since wrapping up the Kenshi Yonezu 2025 TOUR / JUNK in April, you’ve likely spent much of the past few months focused on creating. After completing such a large-scale tour, including overseas performances, has there been any changes in your mindset?

Experiencing concerts in countries I’d never been to before on the world tour, in Korea, the U.S., and various cities in Europe, was huge for me. I don’t want to sound disrespectful to those who’d already been listening to my music outside Japan, but since I hadn’t really thought about it much before, I was surprised by the realization that, “So many people have been waiting for me.” I was welcomed so warmly, and even heard voices calling out “Hachi,” a name I haven’t been addressed by in years, which made me genuinely happy. It left me with a very strong feeling of refreshing clarity.

After going through that, I feel like I’ve started aiming for a more productive way of living this year — something I’d always struggled with before. Looking back on my life, if I hadn’t been accepted through music, I think it would have been terrifying. I wasn’t someone who could function socially, just spending all my time making music or drawing at home, neglecting everything else. But now I feel like I’m gradually moving away from that kind of life. It’s very ordinary stuff, but I’ve started doing simple things like keeping a daily routine and paying attention to my health. For most people it might sound like, “Really? Only now?” But for me, it feels like my way of living has shifted a lot. I can’t say for sure whether the concerts were the direct reason, but I do feel they’ve had a big influence.

I saw your shows in Seoul and Los Angeles, and remember you saying, “I’ll come again” while addressing the crowd. Local fans probably took that as a promise of a reunion rather than a one-time visit, and I imagine that feeling developed for you somewhere along the tour.

Yes, that was almost something that just slipped out. Even when I said I’d come again, there wasn’t a concrete plan in place, so I wondered if it might have been an irresponsible thing to say. But the scenes I saw during the tour were radiant. For the first time in my life, it felt like I was truly making eye contact with the audience.

Now, tell us about “IRIS OUT” and “JANE DOE.” After you were asked to work on CHAINSAW MAN – THE MOVIE: REZE ARC, where did the production of the songs begin?

It started with the request to create two songs. One was already decided to be the ending theme, and for the other, the production team was exploring where it would fit within the film. From the beginning, I had a strong, specific idea of what I wanted “JANE DOE,” the ending theme, to sound like. But with “IRIS OUT,” I remember figuring things out as I went along while creating it.

Having written “KICK BACK” for CHAINSAW MAN before, were you mindful of any links between that song and the new ones?

From the start, I felt strongly that I didn’t want it to turn into something like “KICK BACK Part 2.” I never really felt that risk with “JANE DOE,” but with “IRIS OUT,” I sensed that if I let my guard down, it could easily end up becoming “KICK BACK Part 2.” So I placed a lot of importance on how to differentiate it from “KICK BACK.” It’s a song with a complex and eccentric structure, full of dynamism, so if that’s like a rollercoaster, then I wanted “IRIS OUT” to be more like a free-fall ride — starting with a jolt, racing straight ahead, and ending abruptly. I was very conscious of giving it that kind of decisiveness. 

“IRIS OUT” feels like a song with a deliberately narrow focus, in the best way. It seems to reflect how Denji is led around as a character. How do you see it?

Since CHAINSAW MAN – THE MOVIE: REZE ARC features Reze as such an important character, I thought it’d be better to keep the focus on the relationship between Denji and Reze. In CHAINSAW MAN and in Tatsuki Fujimoto’s manga in general, there are often women who throw men off balance. I think that’s one of Fujimoto’s hallmarks as a writer, and the “Reze Arc” is very much a story where that nuance stands out. So it felt necessary to keep everything centered on Denji being enthralled by a woman named Reze, who is such an alluring and beguiling woman. By honing in on that single axis and driving straight into it, I felt I could differentiate it from “KICK BACK.”

What do you think makes Reze so appealing?

It’s that she playfully unsettles and misleads him in a way that’s somehow enjoyable. She blushes, casts an upturned gaze at Denji, and teases him a little while making her affection for him unmistakably clear. Of course someone like Denji would fall for it, and in a way, the desire to be deceived is actually an important aspect of romantic feelings. She’s charming and mischievous, but at the same time has a certain mysterious quality — you never really know what she’s thinking. If someone asked, “Who is that girl?” the truth is, no one really knows. She’s the kind of presence that unsettles your senses in the most pleasurable way possible.

Tell us about “JANE DOE” as well. Since it was intended to play during the ending of the Reze Arc movie, what was your initial concept for the song?

At first, I thought it probably shouldn’t be me singing. My male voice didn’t feel at all appropriate for the ending of the Reze Arc movie. I had a strong sense from the start that the song needed to be led by a female voice to work properly. I really like the duet “I’ve Seen It All” by Björk and Thom Yorke from Dancer in the Dark. I felt that kind of nuance would fit perfectly, and started creating the song with that in mind. From there, there were various twists and turns — I even tried a version that was nostalgic and evoked youthful feelings — but it felt overly circuitous. In the end, I felt that a duet with a slightly melancholic, dark vibe would be the most fitting. That’s how it came together.

You mentioned in your comments that you didn’t have a specific singer in mind when you began writing it. At what point in the songwriting process did you imagine Hikaru Utada for the track?

I started from the piano riff, and when the melody and lyrics for the first verse began to take shape, I was thinking it had to be Hikaru Utada. My personal impression of their voice is that it can be melancholic, wistful, and lonely, while at the same time — including their smoky tones — it has a freshness that sweeps through like a breeze. They have both qualities. Also, when listening to their music, there’s a sense of being overpowered by their immense talent and the brilliance of their songs and voice. There’s both a tremendous presence and a certain ethereality in their inner world. I even felt that without that duality, the song wouldn’t work.

Hikaru Utada is an extremely multi-faceted artist, and throughout their career they’ve given form to many different expressions. With “JANE DOE,” it feels like the sense of loss that often appears in their work is being drawn out. What are your thoughts on that?

Two of my personal Hikaru Utada favorites are “FINAL DISTANCE” and “Dareka no Negai ga Kanau Koro.” I first heard those songs in junior high, and they were the starting points for Utada-san’s presence becoming a big part of my life. I went to one of their concerts recently, where they performed the original “DISTANCE” in a remixed version. It was presented with a happiness and overflowing sense of euphoria that stood in contrast to “FINAL DISTANCE.” They were singing “hitotsu niwa narenai” (though we can’t be one) while dancing joyfully, and I thought it was wonderful. This is just my personal impression, but I feel that kind of duality, ambiguity, and kind of helplessness is something that lives strongly in their music. I felt there was something in common with what Reze embodies. Of course, I’m not saying Utada-san is like Reze.

You sing from Denji’s perspective in “IRIS OUT.” Listening to “JANE DOE,” it almost feels as if Utada is taking on the role of Reze. Was that intentional?

I explained to Utada-san that I wanted to create a duet between a girl carrying something incredibly complex and a boy who essentially doesn’t understand that at all, and asked them to sing it in that way. They approached that with their own take and that’s how it took shape.

What did you communicate with Utada in terms of recording and production?

Since they live in London, the recording process was carried out by exchanging data, almost like corresponding back and forth in letters. We did have one phone call, and during that conversation they told me something along the lines of, “I think if you sing it this way, your voice will stand out more.” I really felt they were right. That’s because Utada-san and I have very different sensibilities when it comes to singing. They’re a musician rooted in R&B and other styles that move with a laid-back, rich sense of rhythm. On the other hand, I come from a background in Vocaloid and computer-generated music, where I tend to place more importance on the vertical grid lines. I can also lean into an alternative rock-like urgency. Since we’re so different in nature, when Utada’s voice is layered onto something I’ve written, it makes the song feel much more full-bodied. That difference between us was really wonderful. As I mentioned earlier, the song ended up embodying the contrast between a girl carrying something deeply complicated and a boy who, at heart, doesn’t understand any of it. That wasn’t something we set out to do at all — it just happened as a result. But it feels like we arrived at the one and only way it could be.

The lines ”Let’s fill this world with mistakes“ in “JANE DOE” and “In this world right now, you’re my one-and-only perfect answer” in “IRIS OUT” feel deeply connected. Were you aware of contrasting or linking the two when you were writing them?

Not at all. When I’m writing a song, I’m completely absorbed in it, so I often only notice connections later on. Even with the title of “JANE DOE,” I realized later that it ties to a song in the Reze Arc movie — a Russian song that Reze sings alone in the story, which includes the line, “Jane slept in a church.” I only noticed that after finishing the song. I find it interesting when these kinds of unconscious links emerge naturally.

—This interview by Tomonori Shiba first appeared on Billboard Japan