On his day off, a young man is killed in his home by a gas explosion, without anyone knowing, having no close relatives. In another world of tall, treacherous mountains and deep oceans, there stands one, massive supercity, stretching throughout the largest mountain range, and across several great chasms, the bottom of which submerged in water. Here, in the Gravel district, lives a young girl surviving on her own. Though one day, in a theft gone wrong, she is shot dead by a cruel patrolman.