Based on a Japanese light novel series written by Mamizu Arisawa, with illustrations by Kanna Wakatsuki. The series originally started serialization in volume seventeen of ASCII Media Works' now-defunct light novel magazine Dengeki hp on April 18, 2002. Four more chapters were published until the first bound novel of the series was released, though more chapters were later serialized in the magazine. Fourteen main novels, plus two additional bonus novels with illustrations by Mari Matsuzawa, were published by ASCII Media Works under their Dengeki Bunko label between January 10, 2003 and December 10, 2008.