Deerhalt hails from the affluent upper urban zone known as Top. He reaches out to Aki Tesno, a skilled AT operator from the impoverished lower valley, commissioning her to locate and rescue a kidnapped Top girl. This mission requires navigating the abandoned structures designated as "the island." Deerhalt's role as an affluent employer from the upper layer stands in contrast to Aki Tesno's status as a "Bottomer" scavenger.