a 160-page guide book titled was published on december 10, 2005 by ascii media works. two more guide books were published by ascii media works for the anime adaptations: on october 27, 2006 with 176 pages, and on october 19, 2009 with 168 pages. four 128-page art books illustrated by ito were published by ascii media works: on february 25, 2005, on august 9, 2007, on august 10, 2009, and on august 9, 2013.