Kore wa Zombie desu ka? or Korezom as it is officially abbreviated, is a story by Shinichi Kimura, with illustrations by Kobuichi and Muririn. The plot revolves around a boy named Ayumu Aikawa who was murdered by a serial killer and later brought back to the world of the living by a necromancer named Eucliwood Hellscythe. Sadly poor Ayumu is not alive, he is a zombie and on his zombie adventures he runs into a Magical Girl named Haruna.
It was at this ill-fated meeting that our hero Ayumu accidentally steals Haruna’s powers and takes them into himself. Now when Ayumu is not being all zombie and stuff he can also transform into a demon slaying Magical Gender-Bender complete with fluffy bows, pink dress, and big-ass chainsaw named Mystletainn.
Kore wa Zombie desu ka? is also an anime created by Studio Deen and it is currently airing in Japan. The show was picked up for 12 episodes that began airing on January 11th, 2011 and there is a special OVA 13th episode planned that will coincide with the release of the 8th novel in June 2011. You can catch this anime on the Crunchyroll website.
Read more about it here: http://newtype.kadocomic.jp/zombie