The Grace Field House stands as a pristine, isolated sanctuary surrounded by a dense, fog-choked forest that no child has ever dared to cross, hiding a nightmarish reality behind its white walls. To the thirty-eight unsuspecting orphans, the world outside is a promised land of adoption and happiness, but the truth is far more gruesome: "adoption" is merely a shroud for a systematic harvest, where children are delivered into the waiting clutches of demons. This horrifying secret remains guarded by the orphanage’s warden, Isabella, whose maternal affection is a calculated mask. The burden of this truth lies solely with thirteen-year-old Megumi, who—having witnessed his own mother leading a terrified child to their slaughter—is forced to play the part of a compliant son while harboring a paralyzing, lethal secret. As he watches his best friends, the optimistic Yuji and the fierce Nobara, blissfully dream of a future that has already been stolen from them, Megumi must navigate a treacherous psychological war against the very woman he calls "Mama," knowing that every day they remain within these walls, the perimeter is tightening and their time is rapidly running out.