Chitoseoni

Oni—undying demons hiding in the human world. To become immortal, a human must kill an oni and take on its mantle. A man commits himself to immortality to change his country, a girl leaps from a height to prove her immortality to a friend, and a primordial oni reappears to save humanity. This omnibus follows the emotional arcs of those demons and humans in the orbit of the oni called Ohka, who has watched over humanity and oni for a thousand years.