Hinako, younger sister to Koushi, suffers chronic illness caused by factory pollution in the Capital. After their mother's death, Koushi accepts factory owner Yuoshichi Okibi's offer: they move into the Okibi household where the family doctor, Takimi, provides Hinako's medical care. This arrangement hinges on Koushi conducting research to enhance bottled lightning and harness skyfire. Hinako's fragile health drives Koushi's cooperation with Yuoshichi. She endures a long wait for the return of her Fire Hunter father and his hunting dog, Kanata.