Leviathan

is a Japanese light novel series written by Eiji Otsuka, with illustrations by Yu Kinutani. The series began publication on January 10, 2004 by ASCII Media Works under their Dengeki Bunko publishing imprint.

Synopsis
Tokyo has reached the millennium with the year of the Showa era, without the great king of fear falling. Suspicious shadows were creeping into this city one after another. Satsuki Fukuyama is a trainee at St. Vallesios University Hospital. Her former lover, Kohei Mitsumi, has been lost since she was assigned to a remote area as a volunteer. One day Satsuki reunites with her former teacher, Midori Nanayama.