Mahou Chuunen

Who are the "ossans" who wield magical wands and transform into powerful fighters!? In a world where magical girls' fighting is a form of entertainment, there are "middle-aged" men who deal with the powerful enemies that the girls can't handle... This is a magical story for all the ojisans and middle managers who struggle in the shadows of society!

(Source: Hakusensha, translated)

Note: Based on the self-published manga by Maki.