Making-of available in the artist's Youtube channel:
・Long version (4h 4min): https://www.youtube.com/watch?v=kOzwgopUbZE
・Short version (30s): https://www.youtube.com/watch?v=aCAw4nJtS-0
・Archived short version: https://danbooru.aniworldai.org/media_assets/20228039