After a catastrophic event devastates humanity, monstrous creatures threaten the survivors. Within a secluded haven, children are raised in peace, shielded from the dangers outside. Yet, some youngsters yearn to explore the unknown world beyond their sanctuary. Meanwhile, in the desolate exterior, youths Maru and Kiruko unite in a quest for a fabled sanctuary known as Heaven, driven by personal motives. Bearing haunting pasts and hidden sorrows, the duo seeks solace and understanding amidst a world scarred by tragedy and mystery.