Owari no Seraph

After losing his parents, eight-year-old Yuuichirou Amane finds himself at the Hyakuya Orphanage, where he struggles to connect with his new "family." But things take a dark turn when a deadly pandemic wipes out everyone over the age of 13. Seizing the opportunity, vampires that had been lurking underground emerge and enslave the remaining humans, treating them like livestock for blood. Fast forward four years, and Yuuichirou and the other orphans have adapted to life under the vampires' oppressive rule. Despite this, Yuuichirou is determined to wipe out all vampires and put an end to their tyranny, which often puts him at odds with his friend Mikaela Hyakuya. Mikaela believes in using cleverness and strategy to survive, and he manages to gain the trust of some high-ranking vampires, which helps him devise a plan for escape. However, their attempt is thwarted by a vampire officer named Ferid Bathory, who brutally slaughters most of the group. Yuuichirou is the only one who manages to escape to the surface, where he encounters the Moon Demon Company, a military group focused on hunting vampires. Eager to take revenge and fulfill his dreams, Yuuichirou jumps at the chance to join them.