Story
Suddenly one day, the world was destroyed by an unknown virus.
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Only children survived.
And those children were ruled by vampires who appeared from the abyss.
Yuichiro Hyakuya was surviving by giving blood to vampires, together with Mikaela Hyakuya and other orphans who shared bond similar to a real family.
Yuichiro could not endure being treated like livestock anymore, and tried to escape to the outside world along with Mikaela and the young orphans.
Four years later.
Yuichiro has enlisted in the "The Moon Demon Company", a Vampire Extermination Unit of the Japanese Imperial Demon Army. He devotes himself into fighting against formidable vampires!!
Same animation studio. Same basic concept - after humanity has degraded, one species has pretty much overcome the human race - Titans in AoT, Vampires in OnS. A young guy (Eren, Yuuichirou) vows to kill all of the members of the threatening species (Titans, Vampires) in a quest for revenge for dead loved ones.