Saito revealed that Studio Chizu was offering the foreign distribution rights to the film during the Cannes Film Festival in May, and that the film is already slated to open in 57 countries, with negotiations underway for North America and France. Saito added that the deals include a requirement to screen the film in theaters first, in addition to broadcast and streaming rights. Charades — a new international sales banner launched by Carole Baraton (formerly at Wild Bunch), Yohann Comte, and Pierre Mazars (formerly at StudioCanal) — represented the film at Cannes. Comte handled sales on Hosoda's previous film The Boy and The Beast when he was deputy head of sales at Gaumont.
Saito also revealed that the movie's runtime is around 100 minutes. He noted that while people might think a shorter runtime makes the movie easier to make, that is not actually the case. Auditions are currently ongoing for voice talent.
Hosoda clarified that he keeps making works with a family theme because he is not done writing about the topic, and said that it can't be portrayed in one work alone. He added that even if the film is produced in Japan, it has a universality to it that will appeal to the foreign market.
Australian anime distributor Madman Entertainment streamed the teaser video for the film with English subtitles on Thursday.
The film's story centers around a family living in a small house in an obscure corner of a certain city — in particular, the family's spoiled four-year-old boy Kun-chan. When Kun-chan gets a little sister named Mirai, he feels that his new sister stole his parents' love from him, and is overwhelmed by many experiences he undergoes for the first time in his life. In the midst of it all, he meets an older version of Mirai, who has come from the future.
Hosoda is directing the film at his Studio Chizu, and is also credited as scriptwriter and for the original story. Hiroyuki Aoyama (animation director os The Girl Who Leapt Through Time, Summer Wars, and The Boy and The Beast) and Ayako Hata (key animator on the same films) are returning for this new film as animation directors. Yohei Takamatsu and Takashi Omori, who Hosoda had previously worked with on The Boy and The Beast, are also returning as art directors for the film. Producer Yuichiro Saito is also returning from Hosoda's earlier films.
Hosoda previously stated that the new film is inspired by his own experience as a father, noting that "Mirai" (which can be translated as "future") is the name of both the sister character in the film, as well as his own daughter. He stated that the conflict in the film echoes his real-life experience of his eldest child feeling that his new sibling "stole her parents, which made her ferociously jealous." He acknowledged that the new film is closer to the human drama of The Girl Who Leapt Through Time and Wolf Children than the action stories of Summer Wars and The Boy and The Beast.