Manga by author Narita Imomushi

Astra L. Doomsday, former captain of the royal knights has finally achieved his dearest wish: To retire and use his savings to get his very own house. But not long after finally arriving to his sanctuary, a young girl crash-lands into his house. The girl is an apprentice witch, and seems to mistake Astra for someone else..... It's astory of a retired knight captain and his witch-in-training loli!!!