Jashin ni Hirowareta Seijo ga, Mouichido Hatsukoi o Torimodosu made

"Prince, I want to live and see you again...!" Cecil, a true saint, is oppressed by her stepmother and stepsister, and prays in place of her stepsister who pretends to be a saint. One day, Cecil is abandoned by her stepsisters in a valley where an evil god lives. There, she is rescued by the evil god Zero, who pressures her to make a contract to become his saint. In order to meet the prince she loved as a child once again, Cecil makes the contract to become the evil god's saint, but...? The abandoned saint's fateful reversal and love story begins!

(Source: Kodansha, translated)