>>282211057
It was going to be a Doremi movie, but they wanted to present it to a wider audience. I'll just copy and paste the wikipedia section for your convenience, so you can have as much context as possible.
Sato was initially going to have the film centered on Doremi and the other main characters of the original anime as adults, with a "miracle" happening through a time paradox. After pitching the idea to Umakoshi, Umakoshi suggested focusing on a wider age appeal; he voiced concerns that since Doremi and her classmates were the same age, this would alienate viewers who would not relate to the characters due to not being in the same age range. Similarly, Yamada, who also wrote the Ojamajo Doremi 16 light novel series, elaborated that an earlier idea for the film would be about a 20-year-old Doremi trying to dig up a time capsule she and her friends buried during their elementary school graduation ceremony, only to find that it is missing, starting a search of what happened on the day it disappeared. He stated that while the story would have appealed to fans of Ojamajo Doremi, it would not have appealed to a general audience. Seki then researched concerns that from women in their 20s would have about their daily lives in order to find common ground. After agreeing to focus on a general audience instead of only Ojamajo Doremi fans, the staff created Sora, Mire, and Reika as the main characters with varying ages to show their generational differences. Approximately 100 women and men participated in the survey and the results were given to Yamada.
Yamada stated that Sora, Mire, and Reika were not based on anyone, and that each character borrowed traits from the main characters of Ojamajo Doremi: Sora wore glasses like Hazuki and had Doremi's "teacher" personality; Mire had Onpu's outspoken personality and was also a returnee like Momoko; and Reika had Aiko's responsible personality, Hana's face, and a tendency to fall in love with terrible men like Doremi.
