Ogre Slayer summary: A mother oni once bore a child that, though humanoid in appearance aside from lacking an oni's horn, bore a sword named "Onikirimaru," or Ogre Slayer. This child was never given a name and is only known by their weapon. Despite appearing human, they are a purebred oni. The belief that they can only become human by ridding the human world of all oni has led them to embark on a lifelong mission to slay their own kind. The oni, still traversing their birthplace of Japan to this day, seeks to vanquish every last oni and eradicate their kind from the world.