Yes, I'm a Magical Girl.Ayumu Aikawa is a zombie resurrected by the necromancer Eucliwood Hellscythe after being killed by an unknown assailant. A month later Eucliwood is now living with Ayumu as he continues to search for his killer. While searching a graveyard, Ayumu encounters a chainsaw-wielding "Masō-Shōjo" (Magical Garment Girl) named Haruna fighting a giant demon bear known as a Megalo, cutting through Ayumu to defeat it. Haruna attempts to erase Ayumu's memories but he inadvertently absorbs her magic, causing her magical costume to disappear, leaving her naked. Haruna decides to stay at Ayumu's house until her powers return. The next day, Ayumu is attacked 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 discovers that he can use Haruna's magic to transform into a Masō-Shōjo, costume and all, to finish him off. After being seen by his classmates wearing Haruna's frilly costume, Ayumu is humiliated. Ayumu is informed by Haruna he must fight the Megalos in her place.