A total of twelve full length volumes have been released from September 18, 1998, to August 20, 2010. In parallel to the twelve volumes, nine autoconclusive light novels of the series (which form the short story collection) have also been published from December 17, 1998, to August 20, 2011. Finally two more volumes titled "Side Arms" focusing on the past of some characters (which form the side story collection) and the birth of Mithril and Amalgam have been published on April 20, 2004 and July 20, 2006. In contrast to the full length volumes, short story collection focuses on the comedy elements from the series. In January 2010, Gatoh wrote another of these stories in celebration of "Gekkan Dragon Magazine"s 300th issue, which has been included in the last short story collection volume. Another series of spin-off novels has been released by Naoto Ōguro with supervision of Shoji Gatoh from August 20, 2011 to February 20, 2016, consisting of thirteen volumes and set years after the original series' ending. The light novels have also been adapted into various manga, as well as three anime television series and an OVA episode for which Gatoh was also part of the staff.