Maou-sama to Kekkon shitai

The demon queen quite by chance saves Haru, a young human boy about to be sold as a slave, and takes him back to be her attendant. Some years later, a bored demon queen asks our now fully grown and handsome Haru what else she has left to do. "Marriage," Haru replies. A heart-pounding love comedy between an innocent demon queen and her servant.

(Source: Flex Comix, translated)