Taiyou no Futago Mahou Shoujo Rin to Mayura ~Senshi no Shikyuu wa Oeki de Mitasare Ma o Haramu~

The earth opened and from its depths came the VIVO, giant world-enders immune to humanity's weapons. Unable to fight, the people of Tokyo built a massive barricade hoping to keep the giants at bay. But it only delayed the inevitable. The barricade was breached; all humans were r*ped or slaughtered. [From DLsite English]