In the Kingdom of Ernesia, it is customary for members of the royal family to marry a "Saint," a woman blessed with mysterious powers. Kate was born as a Saint in this kingdom and is engaged to the second prince, Gilbert. However, for some reason, he has always treated her coldly.

One day, a new "Saint" is summoned from another world. Fearing that Gilbert would break off their engagement, Kate attempts to flee the castle. But the one who offers to help her escape is none other than the newly summoned Saint from another world…!?