Based on a fantasy manga by Narita Imomushi.

Astra Ludger 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 at his sanctuary, a young girl crash-lands into his house. The girl is an apprentice witch and seems to mistake Astra for someone else.

(Source: M-U)