Filia was a young commoner living alone in the countryside, as her rare appearance kept others away from her. One day, she is found by the royal family, and the king declares, "You are the legendary saint reborn!" From that day forward, she dedicated herself to the kingdom, being in the service of the royal family. However, after just one year, the castle is suddenly attacked by Artel, a demon who is known as the Demon King of Ruin. As a bargain to save the kingdom, Filia is handed over as an offering to Artel. Initially, Artel was a terrifying being, but it seems that he has a surprisingly kind side... However, amidst this warming moment, Artel says, "If you're that desperate to get away from me... I'll have to teach you a lesson." "You are mine, and mine alone, little saint."