Movie 21 guidebook has interviews with
Interviews : http://imgur.com/a/6UmqA
-Aoyama Gosho - 3 pages
-Shizuno Koubun - 2 pages
-Takayama Minami (Conan) - 2 pages
-Horikawa Ryou (Heiji) - 2 pages
-Miyamura Yuuko (Kazuha) - 2 pages
-Yukino Sakki (Momiji) - 1 and 1/2 pages
-Yoshioka Riho (Hiramoto Mikiko) - 1/4 page
-Miyagawa Daisuke (Sekine Koji) - 1/4 page
Additional Momiji and Iori stuff : http://imgur.com/a/0yuP0
Several interesting points in the Aoyama's interview from the M21 Cinema Guide: About M21
• Aoyama drew 6 original scenes for M21. He also revised almost all scenes of romance moments, and checked all scenes involving Kazuha, Heiji, Momiji, Ran, and Conan.
• "When will Heiji confess to Kazuha?" M21 brings about such feeling.
• It was decided before the release of M20 that M21 would be a love story about Heiji and Kazuha. Aoyama wrote it replying some postcards of 2016.
• The idea of using Karuta as the main theme of M21 was raised up around the release of M20.About Ooka Momiji and Iori Muga
• The character Ooka Momiji was designed as a girl from Kyoto that would appear in M21 as Kazuha's love rival, before Aoyama decided to introduce her to manga (on her first appearance). On the M20 celebration on 04/15/2016, Aoyama decided to let Momiji briefly show up in the manga series so that her later appearance in M21 wouldn't seem too abrupt. Aoyama decided her family name to be Ooka, but her given name Momiji was decided by other people.
• Momiji will appear again in the future as a rival. With a very rich and powerful family, she can be considered "the Sonoko of the west
". People can imagine things like her family having bad relationship with Suzuki Jirokichi, which would be interesting.
• Iori Muga was designed by Aoyama, although the character was at first designed to be an old man. It was then changed to the handsome young butler as he is, who's very faithful to Momiji. He's not speaking in a Kyoto accent. About future plots and File 1000
• Both Momiji and Okita Soshi will appear again in the manga.
• File 1000 series will be a big event of the high school boys and girls
. The love story of Ran and Shinichi will take place. Heiji and Momiji will also show up.