lucky ducky's Favorite

Please help. I'm looking for a oneshot manga about a Magicians apprentice who thinks his master is getting married or looking for a wife. So the little apprentice asks his famous sister to marry. Stuff happend we found out the marriage set up was for the apprentice also the apprentice turns out to be a girl. The magician passes her of as a boy. I think they got married once she grew up. Any help is greatly appreciated.