Maru, a teenage boy, crosses a post-apocalyptic Japan with his hired bodyguard Kiruko in search of a place called Heaven, navigating ruins and kaiju-like creatures the locals call Man-Eaters. Inside a walled facility, a group of children have grown up cut off from the outside world, and one of them, Tokio, receives a cryptic message asking whether she wants to go 'outside of the outside'. Her friend Mimihime foresees two strangers arriving from beyond the walls. The two storylines unfold in parallel, their connection revealed in pieces.