Demon Slayer’s head writer reveals how cornerstone of Japanese cinema inspired Infinity Castle

Demon Slayer: Kimetsu no Yaiba – Infinity Castle is a tremendous achievement that required an unfathomable amount of work and skill from the team at Japanese anime studio Ufotable. Not only was Infinity Castle a blockbuster hit that showcases anime’s foothold in America, it’s also a highly entertaining story. For Ufotable co-founder and Infinity Castlelead writer Hikaru Kondo, that last part was perhaps the most difficult to pull off — until he remembered a story about the creation of one of Japan’s most revered films, Seven Samurai.

Infinity Castle thrusts series protagonist Tanjiro Kamado and several of the Demon Slayer Corps into their final, most desperate battle as the Demon King, Muzan Kibutsuji, lures them into the labyrinthine castle. With our heroes scattered across shifting battlegrounds, the film centers on a series of high-stakes, one-on-one confrontations against the Upper Rank demons, testing each slayer’s resolve, bonds, and limits.

Kondo knew he had to pick and choose what to adapt from the manga for the sake of runtime. But he also had to keep the same intensity and impact from the source material to serve his devoted (and nitpicky) audience.

“We’ve got Shinobu, we’ve got Zenitsu two, and then we’ve got Giu and Tanjo all having their own battles in three separate places, three locations, three different battles,” Kondo tells Polygon in a video call, via translator. “Can you name any movie that undertook that level of complexity and pulled it off, and was still interesting?”

While developing Infinity Castle, Kondo worried the film could easily devolve into a series of fight sequences with no real narrative given all the fighting in this arc. The answer came from the behind-the-scenes story of Seven Samurai, and the struggles screenwriter Shinobu Hashimoto and director Akira Kurosawa faced while developing their landmark 1954 movie.

“They made Rashomon together with Ikiru and the Seven Samurai,” Kondo explains, “Before the Seven Samurai was a film, Hashimoto and Kurosawa were trying to make an Omniverse film of eight different samurai warriors on their own journey, and they did everything up to writing the entire screenplay. In Shinobu’s biography, he mentioned they looked at the screenplay and decided, ‘You know, this isn’t a movie. We don’t have a movie here, it’s just action sequences,’ and they shelved the project. And what came of that was the Seven Samurai.”

Kurosawa initially conceived of Seven Samurai as a single day in the life of a samurai, from morning rituals to a fatal mistake that would force him to commit seppuku to preserve his honor. But after extensive research, he abandoned the idea, feeling he lacked enough concrete historical detail. Kurosawa then proposed a different approach: a film built around five samurai battles inspired by real-life swordsmen. Hashimoto began writing that version, but Kurosawa ultimately discarded it as well, concerned that a movie made up of little more than “a series of climaxes” would feel hollow.

The breakthrough came when producer Sôjirô Motoki uncovered historical accounts showing that, during Japan’s Warring States period, samurai would sometimes guard peasant villages overnight in exchange for food and shelter. Around the same time, Kurosawa encountered an anecdote about a village hiring samurai for protection. That idea became the foundation for his film.

“And when I was developing Infinity Castle, going through the screenplay, trying to draw the storyboards. I remembered that little anecdote, and I saw exactly what they were talking about,” Kondo says. “So I am extremely, extremely relieved looking at the worldwide reception and how fans have reacted to the film.”