Yukari Morita is a high school girl on a quest to find her missing father. While searching for him in the Solomon Islands, she receives the offer of a lifetime--she'll get the help she needs to find her father, and all she need do in return is become the world's youngest, lightest astronaut. Yukari and her half sister Matsuri, also petite, are the perfect crew for the Solomon Space Association's launches, or will be once they complete their rigorous and sometimes dangerous training.