How ‘Demon Slayer’ Studio Broke the Laws of Anime Physics to Bring ‘Infinity Castle’ Battles to Life
As io9 detailed, 2025 was a definitive year for anime films, thanks in part to meteoric box-office success Demon Slayer: Infinity Castle. As the film prepares for awards season, its directors shared behind-the-scenes stories about how studio Ufotable pushed its limits (and the laws of physics) to bring the anime’s epic battles to life.
Speaking to Entertainment Weekly, Infinity Castle director Haruo Sotozaki, director of photography Yuichi Terao, and Ufotable president Hikaru Kondo recalled how the studio’s commitment to making the best anime has contributed to the film’s place on the table this award season.
In the movie, hero Tanjiro Kamado and the rest of the Demon Slayer Corps dive straight into enemy territory, fighting off an onslaught of powerful enemies and powerful bosses in the ever-changing maze that is Infinity Castle. Although this is not the case Demon Slayerfirst rodeo in cinemas, Infinity Castle marks the beginning of the end of the banner series as the first of a film trilogy. Having the first leg of that trilogy in IMAX theaters inspired Ufotable to elevate the streaming anime into a cinematic experience. The studio wanted to ensure that every corner of the screen came out with detail, which required collaboration in its integration of 2D characters moving through 3D space in its fluid action sequences.
“If you look at a lot of the keyframes, the key animations, the sakuga in this film, we worked very closely with our 3D department to make sure that everyone was completely locked in because we didn’t want weird weird effects where maybe these 2D characters are sliding around in 3D environments and situations,” Sotozaki told EW. “So it was really important for the 2D keyframe animators to talk to our 3D team to make sure the songs were perfect.”
Of that, Sotozaki told EW that it was the most complicated feature to deliver Infinity Castle in life it ensured that its 3D environments and animations were all synchronized. To prevent oopsies during production, he said, Ufotable will often test keyframes in their 3D environments before finishing key animations. While the secret to hero Tanjiro’s success is his amazing breathing techniques, Terao explained that Ufotable’s animators will entertain themselves with music so that, when pencil hits paper, Infinity CastleMany of the set pieces and the momentum of the sequence will flow directly into the animation.
“Whenever you see Tanjiro saying, ‘Don’t give up,’ it’s probably the animators doing the same thing with their headphones on,” Terao said. “I’m on the digital 3D side of things, but I know this is especially true for the keyframe animation team, the 2D animators. Whenever they wanted the actors to do certain actions, sometimes they would get up from their desk and actually act out some of these action sequences. So if you catch this out of the corner of your eye, sometimes you might wonder, ‘Are they looking for something or trying to dance to what they want. What would animation look like?’ It’s an interesting sight to see.”
So far the biggest obstacle for the team was Infinity CastleThe final battle between Tanjiro and Akaza, which Sotozaki says is led by four people at Ufotable. Chief among them was key animator Masayuki Kunihiro, whom Sotozaki described as handling 80 percent of Akaza and Tomioka’s physics-defying battle.
“It’s really tricky action, but it’s fast action. I mean this in a nice way, but it doesn’t make sense in the sense of how fast the actors can move and how they look on the screen. It’s very convincing to the audience, but it’s against physics,” said Terao. “If you’ve seen the film, you’ll understand what we’re talking about, first of all we try different types of animation in the parts of the film Infinity Castle whether it crashes, breaks, or falls, there is a lot of destruction. And take, for example, when Akaza hits the ground. It scatters and you have this smoke, but all of this needs to be simulated in CG in these different physics engines. “
“The irony is, if you look at Kunihiro’s animation, you’ll flip one frame of paper and the characters will move like 100 meters, which is impossible in real-world physics. So a lot of the simulation that we tried to use was how things disappear, which made that hybrid between 2D animation and 3D simulation very challenging, to get a detailed description,” Sausage was made.
He continued: “It was fun, but it’s a challenge because there aren’t really any settings that allow fast physics to happen the way physics engines use different dimensions. So I think he has a very unique pipeline, too. Usually we’ll have 2D action animators who match the action with a 3D environment or a gun structure, but Kunihiro is the one that’s different and it allows him to do the first 3D key. It has to match 3D Situations in whatever he’s rendering. “
The trio unfortunately said they couldn’t give an update on when fans can expect the second installment Demon Slayer‘s film trilogy is the end or what is the future? Demon Slayer it would seem that if the trilogy ends. This response, in concert with Crunchyroll’s president’s FOMO-fueled “better watch it in theaters while you can” response to anime fans asking when they can expect the movie to hit the streamer, is quite disappointing.
However, Sotozaki assured fans that Ufotable will continue to strive to deliver a consistent level of animation quality in the final legs Demon SlayerEnd of the theater series.
“At the studio, we always try to meet and exceed the expectations of the audience and create an experience that everyone can enjoy and the entire team and crew share this feeling, so do with that knowledge what you will,” said Sotozaki.
In io9’s review of the Infinity Castlewe also praised the film for its brilliant animation and action sequences, writing, “Ufotable’s animation is as brilliant as ever, with smooth camera movements with its characters playing against a 3D CG background, coupled with a fine composition that gives the film a cinematic beauty that surpasses previous films.” Mugen train. Its action choreography is a rollercoaster for the eyes—fluid, explosive, and sometimes slow, as if to let sparks fly from the katana’s blades like fireworks behind your eyes. And its final battle kicks things into third gear.”
Apparently, Ufotable’s reputation as an anime studio to watch has paid off this year, because Infinity Castle received a Golden Globe Award for Best Animated Feature Film. Chainsaw Man – Movie: Reze Arc, despite being equally beautifulHe didn’t make the cut, after all Demon Slayer all you have to do is beat out the other nominees (including heavy-hitters KPop Demon Hunters again Zootopia 2.) Like Issa Rae at the Emmys, we champion anime for everyone.
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