Himesama no Shitto de Youjo ni Sareta Danshaku Reijou desu: Hakkin no Kishi-sama kara no Propose!?

Berna, who works as a maid in the castle, is the occasional conversation partner of Dietrich, a beautiful, otherworldly young man who serves as the prince's guard. After Dietrich's marriage to the princess of the neighboring kingdom, rumored to wield dubious magic, is decided by royal command, Berna is to attend their engagement party as waitstaff. As soon as the princess shows up on the day of the party, she casts a spell on Dietrich, forcing him to propose to his true love in front of all of those in attendance. Berna who working to make sure the proposal went smoothly for Dietrich, is left speechless when he proposes to her instead! Enraged at Dietrich's actions, the princess curses Berna, turning her body into that of a little girl's! Let this love story between a common girl and a stunningly handsome knight commence!

(Source: Square Enix)