Fire demons are a type of demonic entity that appear in the animated film Demon City Shinjuku. When Shinjuku was devastated by the Demon Quake, thousands of innocent people died in the disaster. Many children were also victims of the quake, but were cursed by the evil magic of Rebi Ra to remain upon the mortal plane as tortured, vengeful spirits. Though these spirits take on the forms they had in life, they are merely souls seeking relief from the pain of their terrible deaths.
During the film, Sayaka Rama and Chibi enter the ruins of Shinjuku Park where they find that Kyoya Izayoi has been bewitched by Rebi Ra. Under a trance, Kyoya is in danger of having his life force devoured by the fire demons inhabiting the park. Sayaka encounters one such demon that appears in the form of a small girl, but the child suddenly erupts into spectral flames. A fissure opens in the ground from which a wall of such fire erupts, threatening to kill Sayaka and Chibi.
When Chibi tells Sayaka about the nature of these demons, Sayaka bravely approaches the fire spirits, appealing to the children they once were and trying to calm their rage. Through Sayaka's patience and compassion, the fire demons are calmed and their curse is lifted. The spectral flames vanish and several small lights - the souls of the children that died in the Demon Quake - fall to the ground like snow before disappearing into the hereafter.