<p>After the 'Tyrant King' killed our parents, we managed to defeat him in a *coup d'état*. My younger sister became Empress and I became the Duchess who ruled the beast-infested Northern territory. We took our revenge and my younger sister has become the Empress, so there's only one task left - the oath I made to God right before helping my younger sister. In order to fufill that oath, I'll have to get married. But for someone like me who has never had a relationship before, 'love' is more difficult than war or fighting a dragon. However, the illegitimate son of the tyrant, the Prince, has just proposed a contractual marriage…?