 The production team envisioned Japanese cities as entities, who require physical agents to execute their will and regulate the activities within them. The concept behind the health of a city is based on traditional Chinese medicine in which the smooth flow of a body's fluids nourishes its internal organs. The team equates yōkai with qi, humans with water, and agents of the city (karas) with blood. They integrated Celtic mythology into their concept for further symbolisms, treating the city as the male (yang); and Yurine (ゆりね), the manifestation of its will as female (yin). In contrast, their theory treats the humans and agents as the children of the city and its will, and classifies them as the reproduction system's five major organs. Following the team's vision, the mikuras (evil yōkai) represent the five elements in this system. This idea forms the basis of the relationship between cities and their inhabitants in the show.
