Tsugai no Okite: Moushuu Maou ni Chouaisarete

A solitary peasant girl named Phoria, shunned for her unusual appearance, is shocked when the king proclaims her a legendary saint. After a year of service and adoration, the "Doom Demon King" Artel attacks her kingdom and demands her as a sacrifice. Though feared as a natural disaster, he treats her with unexpected kindness—until his sweet words turn into a possessive vow to make her his alone forever.