With the arrival of a mystery illness that kills everyone over the age of 13, humanity is subjugated by previously concealed, power-hungry vampires who emerge to conquer civilization with the promise of safeguarding the survivors in return for blood donations. Yuuichirou and Mikaela Hyakuya, two young boys kidnapped from an orphanage, are among the survivors, along with other youngsters they consider family. Mikaela, fed up with being treated like cattle under the vampires' brutal dominion, devises a defiant escape plot that is ultimately doomed to fail. Yuuichirou is the sole survivor who makes it to the other side, and he is discovered by the Moon Demon Company, a military organization committed to the abolition of vampires in Japan.