Machimaho

Machimaho: I Messed Up and Made the Wrong Person Into a Magical Girl! (間違った子を魔法少女にしてしまった) is a manga written and illustrated by the mangaka Souryuu in the magazine Kurage Bunch.

Plot
While searching for a brave candidate to become a magical girl and defend the world from evil, a mythical creature finds Kayo Majiba, a cute young lady who seems like the perfect fit. But when this newly turned magical girl proves to be a crude delinquent who goes berserk in a conflict, it becomes clear that this may have been a terrible mistake. Now evil—and any innocent bystanders—will face the rage of a magical girl gone wrong!