Slasher Maidens, Vol. 1 (Volume 1)

Asuma Sudou has always been a proud pervert, but he's sworn to give that up to chase the girl of his dreams. Having received a special invitation to enter the same all-girls school as her, he's planning to live his romantic youth to the fullest. But those plans are cut short when it turns out the school is a front for a secret organization dedicated to battling kaijin-monsters created when people succumb to their murderous impulses! The girls of the school fight using the relics of defeated kaijin, but when the bloodthirsty instincts sealed within threaten to overwhelm them, Asuma is the only one who can bring them back to their senses!