Eclair, the daughter of House Bilro which is one of the nation's four great ducal families, is a top student at the magic academy and a gifted magic knight.

One day she’s serving as a guard at the ceremony to choose the princess’s fiancé. In the middle of the proceedings, a magical device the princess wears suddenly malfunctions and explodes; Eclair throws herself in front of it to protect the princess and is swallowed by a mysterious magic circle. Mistral, the head of House Tamon, rushes to her aid... but Eclair's body has been shrunk...!

The key to breaking the curse? A marriage to the contrary duke!