Where was The Boy and the Heron (2023) filmed?

Director Hayao Miyazaki in 2009

Producer Toshio Suzuki in 2004

Following the release of The Wind Rises (2013), Miyazaki held a press conference in Tokyo in September 2013 announcing his retirement from feature animation, saying: "I know I've said I would retire many times in the past. Many of you must think, 'Once again.' But this time I am quite serious." However, Miyazaki later changed his mind after concluding work on the short film Boro the Caterpillar (2018) and decided to come out of retirement to direct another full-length film; his decision was captured in the 2016 documentary film Never-Ending Man: Hayao Miyazaki. He commenced storyboarding for the film in July 2016 and presented a project proposal for it the following month. This proposal included the children's novel The Book of Lost Things by Irish author John Connolly, which formed "a loose framework" for the project. Edogawa Ranpo's Ghost Tower (幽霊塔, Yūrei-tō), which Miyazaki loved as a child, inspired the tower in the film.

Although initially resistant, Toshio Suzuki approved the project, taking into account Miyazaki's commitment and storyboard work. After Suzuki announced the start of work on Miyazaki's new film in February 2017, the studio's official website posted a call for staff for the new project on May 19, 2017, and production began in earnest. With Miyazaki coming out of retirement, Studio Ghibli reopened, with many of its past collaborators working on the project. At an event held at Waseda University in October 2017, Studio Ghibli announced the film would be titled Kimitachi wa Dō Ikiru ka, after the 1937 novel by Genzaburō Yoshino. Suzuki clarified that the novel is not related to the film beyond inspiring the title. The release date was not determined, but Miyazaki voiced his desire to release the film around the time of the 2020 Summer Olympics in Japan. Suzuki said that Miyazaki was working on the film for his grandson as his way of saying "Grandpa is moving on to the next world, but he's leaving behind this film."

Suzuki stated in August 2018 that the film was expected to be completed in 2021 or 2022. He stated that it was 15% complete at the end of October 2019. In a December 2019 interview with NHK, Suzuki explained that the film was not to be expected anytime soon; Miyazaki in his younger age used to produce 10 minutes of animation every month, but now his speed was reduced to 1 minute per month. Despite talk of Miyazaki's upcoming film being his last, Suzuki doubted it, asserting that as long as Miyazaki lives, he will likely keep making films. Unlike his previous films, Miyazaki did not oversee every single frame and focused on the storyboards, while the animation director Takeshi Honda took charge of the animation process. In February 2020, the studio decided to release some of its previous filmography on streaming platforms like Netflix in order to finance the production. Suzuki convinced Miyazaki to make the deal as he did not use a computer or smartphone and was unaware of online streaming.

In May 2020, Suzuki recounted to Entertainment Weekly that 60 animators were working on the film, and that an estimated 36 minutes had been completed after three years of production, saying "we are still hand-drawing everything, but it takes us more time to complete a film because we're drawing more frames", and they were "hoping it will finish in the next three years". In December 2020, Suzuki stated that the production was working with no deadlines, similarly to The Tale of the Princess Kaguya (2013), which took eight years to make. He said that COVID-19 pandemic restrictions had not stopped production, and that half of the film's estimated 125 minutes were complete. He also revealed that Miyazaki wanted to adapt Diana Wynne Jones's Earwig and the Witch during development, but his son Goro directed the adaptation instead. Cinematographer Atsushi Okui suggested the idea of using Dolby Cinema to Miyazaki during the production of Earwig and the Witch. Okui was particularly drawn to the technology's ability to maintain image sharpness in bright scenes while preventing dark areas from becoming overly black.

In October 2021, Miyazaki told T that he was making the film because he did not have an answer to the question "how do you live?" In October 2022, the chairman of Studio Ghibli  [ja] stated that the film was approaching completion, but did not specify a release date. In December 2022, Takuya Kimura, who voiced Howl in Howl's Moving Castle, "hinted" that he was in the film with a post on social media. Suzuki considered The Boy and the Heron to be the most expensive film ever produced in Japan. The production timeline spanned approximately seven years, comprising two and a half years dedicated to pre-production activities and about five years for the production phase.

GKIDS managed casting for the English version in collaboration with Studio Ghibli. The dub was directed by Michael Sinterniklaas at NYAV Post, and Stephanie Sheh wrote the script. The English cast, unveiled on October 17, features Christian Bale, Dave Bautista, Gemma Chan, Willem Dafoe, Karen Fukuhara, Mark Hamill, Robert Pattinson, and Florence Pugh. Pattinson spent several weeks perfecting a nasal growl in preparation to play the Heron, and was able to record all of his dialogue in two days.