Ringoku no Outaishi ga Dorei to Shite Urarete Itanode Katte Mimashita

Natalie, a candidate for the title of Great Saintess, is framed and condemned by her rival, Florentia, during the selection ceremony. Although cursed to die the moment her divine power runs out, she awakens to the true power of the Great Saintess at the last possible second and barely manages to escape with her life. While visiting a trading house to hire bodyguards for her flight abroad, she finds—of all people—Vincent, the Crown Prince of a neighboring country, being sold as a slave. Sensing trouble but calculating that saving him might secure her protection in his kingdom, she decides to purchase him. However, a shocking truth comes to light after the sale: "Vincent... you weren't meant for gladiatorial combat!?" Vincent bears a bizarre magical mark that inflicts agonizing pain upon him unless he sexually satisfies his master. To alleviate his suffering, Natalie finds herself on the receiving end of "service" from the proud Crown Prince himself...!? Despite being the master, Natalie soon finds the tables turned as she is swept up by the obsessive Vincent in this romantic fantasy! https://mechacomic.jp/books/258724