 Viz released the first 37 volumes on a quarterly schedule, mirror-imaging the artwork to a "flipped" left-to-right format as standard in English-language works, as opposed to the right-to-left reading direction of Japanese.Volume 1 was released on July 6, 1998; volume 37 was released on April 14, 2009.On April 22, 2009, Viz announced that future volumes would be released in an unflipped format on a monthly schedule, starting with volume 38 in July 2009.