Fairy Girls, Vol. 4 by Hiro Mashima

Fairy Tail spins off for a new series featuring just the girls! Erza, Lucy, Juvia, and Wendy stumble upon a group of four female ruffians trying to pass themselves off as genuine Fairy Tail wizards. As they untangle the impostors' plot (with time for a few laughs along the way), the underworld of Fiore is going to learn who the real ruffians are!