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. While searching a graveyard, Ayumu encounters a chainsaw-wielding "Mas?-Sh?jo" named Haruna fighting a giant demon bear known as a Megalo, cutting through Ayumu to defeat it. Haruna attempts to erase Ayumu's memories afterward but he inadvertently absorbs 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 Megalo. Haruna arrives but is unable to summon her magic, so Ayumu uses his zombie strength to pummel the Megalo. He then discovers that he can use Haruna's magic to transform into a Mas?-Sh?jo, costume and all, to finish him off. After landing and facing humiliation from his classmates, Ayumu is informed by Haruna that he is to fight the Megalos in her place.