Mahou Youjo to Kurashi Hajimemashita.

is a Japanese light novel series written by Shishi Ino, with illustrations by Ragho no Erika. The series began publication on October 10, 2013 by ASCII Media Works under their Dengeki Bunko publishing imprint.

Synopsis
The fallen demon master, Yukito, picks up a little girl in the park.

The little girl was a mystery who couldn't take off her clothes by herself and walked around naked after getting out of the bath. Surprisingly, I was fascinated by the magical girl anime. She plays as a magical girl, actually--. If you team up with a little girl, you might be the strongest retired demon !?

The witch girl (?) Demon action, in which a dull boy and a mysterious little girl play an active part, has finally begun!