Shinkai began writing the script for the movie in 2014. He said that he used one of his other movies, "Cross Road" to create the story. The story was inspired by many things. It was inspired by Shūzō Oshimi's "Inside Mari", "Ranma ½", a novel from the Heian period called "Torikaebaya Monogatari", and a short-story by Greg Egan called "The Safe-Deposit Box". Shinkai also said that after the sinking of MV "Sewol" in 2014, he wanted to make a story about a disaster.