This redesign of the original hero was based on Hideaki Anno's desire to revisit Tohl Narita's original design, going as far as to seek permission from Narita's son, Kairi. The first concept art was made by Anno in Octounder the likeness of Bin Furuya, the hero's original suit actor in the 1966 series. The concept is based on an Ultraman painting by the late Tohl Narita in 1983 called “Incarnation of Truth, Justice, and Beauty” ( 真実と正義と美の化身, Shinjitsu to Seigi to Bi no Keshin). Ultraman, the titular hero of the movie, had his design unveiled in Tsuburaya's 2019 convention Tsubucon. The film was postponed in March 2021 due to the COVID-19 pandemic from its original Summer 2021 release. I will solemnly strive to fulfill my responsibility to pass on that heavy, radiant baton created by my seniors." The rest of the cast members were announced in September of that same year. Higuchi commented, "A baton has been entrusted to me that has been shining ever since I was a small child. The film would be co-produced between Tsuburaya Production, Toho and Khara, with an aim for a 2021 release. Masami Nagasawa, Hidetoshi Nishijima and Takumi Saito were named to star in the film.
The project was formally announced in August 2019, with Higuchi as the director and Anno as the screenwriter. The early production was dated as far as February 2019, but Hideaki Anno's participation in Shin Ultraman was a late addition as he was originally involved with the production of Evangelion: 3.0+1.0 Thrice Upon a Time. Other announced cast members include Daiki Arioka, Akari Hayami, Tetsushi Tanaka, Koji Yamamoto, Ryo Iwamatsu, Kyusaku Shimada, Toru Masuoka, Kenshi Nagatsuka, Hajime Yamazaki and Soko Wada. According to Takumi, he has a fond memory of playing with Ultraman figures and his father was one of the crew members behind Ultraman Taro. Takumi Saitoh portrays the man who eventually becomes the human host of Ultraman.