The filmmakers used still frames from the original series Ultraman: A Special Effects Fantasy Series (1966) as storyboards.
Hideaki Anno originally intended to do an adaptation of Eiji Tsuburaya's TV show Mighty Jack (1968), a favourite from his childhood. He instead made an Ultraman film, which Tsubaraya had also created.
Toward the end of the movie, Taki puts down two mugs one of which of them displays a silhouette of Kyubey from Puella Magi Madoka Magica (2011).