Childhood friends Aoi Satsuki and Arata Uzuki are tasked with producing a fan event as part of a TsukiRadi project. Aoi, the considerate and kind prince of Gravi, selects "adventure" as the event's theme.

Believing adventurousness to be something he lacks, Aoi works extra hard to come up with an event concept with Arata. The answer they arrive at is a puzzle/escape room at the zoo that will give guests a taste of the extraordinary. The younger members take on the role of the guests as they begin rehearsing for the event!
That meant go back one letter 
in the alphabet for each one given.
المقصود بذلك هو العودة حرفاً واحداً
في الأبجديّة لكلّ حرف مكتوب
Bei jedem Buchstaben geht man
im Alphabet einen Schritt zurück.
Se refería a retrocer
a la letra anterior del alfabeto.
Se refería a retrocer
a la letra anterior del alfabeto.
Il fallait chercher
la lettre précédente.
Significava andare indietro di una lettera
nell'alfabeto per ognuna di quelle scritte.
Ou seja, voltar uma letra no
alfabeto para cada uma da dica.
То есть подставить буквы, 
которые идут перед ними.