Seraph of the End

From the introduction: On the 25th December 2012, the world came to an end. A mysterious virus spread throughout the world, killing all full humans above the age of 13 and, not long after, the endless hordes of the Horsemen of the Apocalypse first emerged, terrible monsters that seemingly have no desires other than killing all humans they come across. Those children who survived amidst the chaos soon came into contact with the vampires, who, emerging from their hidden cities deep below the surface, enslaved the survivors for use as little more than livestock. Seeing as even the weakest vampire is many times stronger than the best of humans, it wasn’t long before most of the surface world was under their control.