Yonige Seijo no Nidome no Kekkon

Saint Seraphina, born to pray and protect her country, follows her destiny and marries the hero Dominic in a loveless marriage. Treated with contempt by those around her and exploited for her holy powers, on her wedding night, she defeats her arrogant, worthless husband, flees the country, and decides to live freely under the Demon King Welhart! A strong and beautiful saint and a lonely, kind-hearted demon king. A reversal love story of two people who give up their destinies and choose to fulfill their dreams!

(Source: Kodansha, translated)