After an exhausting day juggling jobs, Gain awakens in a suffocating darkness, trapped in an inexplicable void. Unable to control his surroundings, he’s plunged into an unsettling encounter with a mysterious figure before being jolted awake by his sister’s voice. But the girl standing before him isn’t the 17-year-old Saya he remembers—it’s an 8-year-old version of her, and worse, his own body has regressed to that of a child.