Based on the novels under the same name.

Aikawa Ayumu is a normal high school boy. One day he is killed by a serial killer and revived as a zombie by a necromancer Eucliwood Hellscythe. He starts to serve Eu as her guard but he happens to deprive a maho shojo Haruna of her magic power. Haruna orders Ayumu to fight against anti-mahou shojo system "Megalo" in her place.

(Source: Mangaupdates.com)