Yes, I'm a Masō-Shōjo

Ayumu Aikawa is a zombie who was brought to life by the necromancer, Eucliwood Hellscythe, after being killed by an unknown assailant. A month since then, Eucliwood has been living with Ayumu as he continues to search for his killer. Whilst searching a graveyard, Ayumu encounters a chainsaw wielding 'masō-shōjo' named Haruna fighting a giant demon bear, cutting through him to defeat it. Haruna attempts to erase Ayumu's memories afterwards but his zombie nature ends up cancelling out her magic. Haruna decides to stay at Ayumu's house until the matter is resolved. The next day, Ayumu is approached by a crayfish like demon known as a Megalo. Haruna arrives but is unable to summon her magic, so Ayumu uses his zombie strength to pummel the Megalo. He then uses Ayumu's magic to transform into a masō-shōjo and finish him off. After landing and facing humiliation from his classmates, Ayumu is informed by Haruna that he is to become a masō shōjo in her place.