Making-of available in the artist's Youtube channel:
・Long version (3h 42min): https://www.youtube.com/watch?v=Rui1QmcKyrs
・Short version (30s): https://www.youtube.com/shorts/LVHaJ2zJNp8
・Archived short version: https://danbooru.aniworldai.org/media_assets/20228770