The Grand Princess Was Not There

In accordance with a promise made with the imperial kingdom of Terrapema, the Grand Duchy of Patria is obligated to marry at the behest of the Crown Prince when the Grand Princess turns 15. However, the time of the marriage is approaching but the identity of the Grand Princess is unknown. In a rural village in Patria, Lapis, the cutie of a family, suddenly finds herself studying to enter the court bridal school. Entangled by the trickery of adults in the background, how far can this innocent girl go?