From the introduction:
Welcome to the Drainage City, the metropolis beneath. The city above is significantly advanced, comparable to most toku settings with its total-conversion cyborg soldiers and strange human remodeling experiments. Of course most of the stuff is kept hidden on the surface, so where do the demons ,the human-animal hybrids, the freaks robots and obvious cyborg monsters make their homes? In the city below! Down in the endless labyrinth of massive flood canals, sewers, forgotten sub basements and various forms of catacombs the city beneath the city thrives off the waste of the city above power, water, scrap everything discarded and lost from the city above comes down here. Anyone can come here willingly, seldom do they as long as we have a choice.