1. Although not stated, the author had in mind that Madalen is studying fashion design.
2. Jio's name is derived from the first names of himself, his dog, and his father (Father's name is Ornesto).
3. The name of the demon comes from the initials of the seven deadly sins in Greek.
4. The characters' hair colors represent their personalities.
5. The book took seven years to complete, with many chapter changes.
6. Joe also had diaries, but this chapter was removed.
7. The book is inspired by a Korean video clip, anime, Alice in Wonderland, Peter Pan, and an escape room themed on the seven deadly sins.