When Myne brings up wanting to become an apprentice priestess to her family, she learns the truth about the role and what it entails, and soon comes to realize that she is in for the fight of her life.

This OVA includes two side stories in it.

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.