When a mysterious virus appears that kills everyone over the age of 13, humanity is enslaved by previously hidden, power-hungry vampires. They emerge to subjugate society by promising to protect the survivors in exchange for donations of their blood. Among these survivors are Yuuichirou and Mikaela Hyakuya, two young boys taken captive from an orphanage along with other children they consider family. Discontent with being treated like livestock under the vampires' cruel reign, Mikaela hatches a rebellious escape plan that is ultimately doomed to fail. The only survivor to come out on the other side is Yuuichirou, who is found by the Moon Demon Company, a military unit dedicated to exterminating vampires in Japan. Many years later, now a member of the Japanese Imperial Demon Army, Yuuichirou is determined to take revenge on the creatures that slaughtered his family, but at what cost?