Seraph of the End: Vampire Reign

With the appearance of a mysterious virus that kills everyone above the age of 13, mankind becomes enslaved by previously hidden, power-hungry vampires who emerge in order to subjugate society with the promise of protecting the survivors, in exchange for donations of their blood. Among these survivors are Yuuichirou and Mikaela Hyakuya, two young boys who are taken captive from an orphanage, along with other children whom they consider family.