Eustachius no Shitamachi Sennyuu Dai Sakusen (Eustachius' Incognito Operation Downtown) To get more information about Myne and her strange background, Head Priest Ferdinand sends two nobles, Eustachius and Eckhard, to investigate everything regarding her life within her hometown. However, things do not go the way they expected. Corinna-sama no Otaku Houmon (Visiting Missus Corinna) Otto's wife, Corinna, takes an interest in the outfit that Myne wore at her baptism. Corinna summons her alongside her mother, Eva, and sister, Turi, wishing to know the procedure in making such sophisticated attire and accessories. Naturally, for Myne, she sees an excellent opportunity for profit.

Recap episodes released before third season, summarizing first two seasons of Honzuki no Gekokujou: Shisho ni Naru Tame ni wa Shudan wo Erandeiraremasen.

Winter is approaching, and Myne—now an apprentice priestess—must prepare for her stay at the church and the upcoming Dedication Ceremony. However, due to her immense knowledge and extraordinary amount of mana, she has garnered the attention of many dangerous people, who are willing to do anything to get their hands on Myne. To keep her safe, the Head Priest assigns Myne a bodyguard and advises her to be adopted by a noble, a decision that will force her to leave her family behind. As Myne is opposed to the idea, the Head Priest gives her an ultimatum: she can be with her family until she turns 10, but if she is deemed too unstable, she will immediately be dealt with. Placed in a tough position, Myne is uncertain about her future. Despite the twists that may lie ahead, she will do whatever she can to protect those that she loves—even if it means giving up on her dream.

Urano Motosu loves books and has an endless desire to read literature, no matter the subject. She almost fulfills her dream job of becoming a librarian before her life is ended in an accident. As she draws her last breath, she wishes to be able to read more books in her next life. As if fate was listening to her prayer, she wakes up reincarnated as Myne—a frail five-year-old girl living in a medieval era. What immediately comes to her mind is her passion. She tries to find something to read, only to become frustrated by the lack of books at her disposal. Without the printing press, books have to be written and copied by hand, making them very expensive; as such, only a few nobles can afford them—but this won't stop Myne. She will prove that her will to read is unbreakable, and if there are no books around, she will make them herself!