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: Comic Meteor)
Note: Chapter count includes 2 extras.