Fifteen years ago, a catastrophe devastated human civilization, and now perilous, man-eating monsters wander the ruined lands, presenting an existential danger to the few survivors left. In the midst of this chaos, a secluded facility protects children, raising them in tranquility. Yet, as some of them learn of the world outside their nursery's limited boundaries, their curiosity regarding it gradually intensifies. Meanwhile, in the outside world, young survivors Maru and Kiruko join forces to seek a special location known as Heaven, each driven by their own motives. Bearing past burdens and tragic secrets, the pair hopes to uncover answers to the cruelty they have endured in their lives and in a world that remains in shambles.