"Once upon a time, fairies were used as weapons of war." The novel is set in a world where fairies possess and live in animals, endowing them with magical abilities. Fairies can be summoned as an alter ego and used as a weapon by extracting the organs of a possessed animal and grafting them into people. Individuals who utilized fairies as war instruments were known as "Fairy Soldiers," and after the conflict was finished and their missions were accomplished, the soldiers lost their purpose. Some began working for the government, some joined the mafia, and still others became terrorists as they pursued their own path in life. The conflict has been over for nine years. Mariya, the protagonist, is a new recruit of "Dorothea," an agency that investigates and prosecutes criminals.