After a mysterious virus wipes out ninety percent of humanity, vampires emerge from the recesses of the earth to enslave mankind, treating them like livestock. After growing tired of donating blood in exchange for protection, 12-year-old Yuichiro Hyakuya and his best friend Mikaela Hyakuya plot an escape along with the other orphans. After being the only successful runaway, Yuichiro joins the Moon Demon Company, an extermination unit of the Japanese Imperial Demon Army dedicated to killing off vampires.