In a world where the war between humans and demons (magical beings) never seems to end, one day, the Demon King Gil arrives at Hazelbart Kingdom, the strongest of all human kingdoms. Gil presents a shocking proposal — a truce and peace treaty between the world of humans and the world of demons, on the condition that both sides respect each other's territories and never cross the border. Seeing this agreement as a chance to elevate her own son's status, the kingdom's second queen secretly hatches a devious scheme. As a result of her plot, Princess Estelle is chosen as the sacrifice — forced to marry the Demon King as a condition to seal the peace treaty… Suddenly, Estelle finds herself the bride of the Demon King — a man completely foreign to her world, with a cold expression and mysterious intentions.