Maou to Yusha no Kyoudai Kankei

is a Japanese light novel series written by Kuchiba Kuroba, with illustrations by Hyakuen Lighter. The series began publication on October 10, 2012 by ASCII Media Works under their Dengeki Bunko publishing imprint.

Synopsis
Kei Amagi, a boy who was feared as a "demon king" in junior high school because of his strength. I spent serious days in high school not to bother my cute little sister.

However, since the younger sister who entered the same high school was discovered to be a "hero" and was also used by a Loli girl called "Ash Witch", Kei's life derailed into a strange extraordinary life. It was ...!? A loose, comical, slightly enthusiastic story of "The Devil and the Hero".