A teenage girl working with a search and rescue, Sona rides 4.4 meter bipedal robot (Mountain Crawler) in the park inside the demilitarized zone between North and South Korea. After long and hard searching, she rescues a lost girl in the mountain but she has to leave Mountain Crawler behind because its battery is depleted. Deserted in the winter woods, Mountain Crawler kills and intakes rabbits to prevent its battery from complete depletion so that it can protect its identity of the AI, which will be force-updated in case of rebooting. The incident was received with a shock by the manufacturing company. The company sends pilots’ psychiatrist to investigate the psyche of Sona and Mountain Crawler behind the accident. She finds out that the robot has a strong will to maintain its identity to keep the special relationship with its pilot, Sona.