The manga has been adapted into an original video animation (OVA) produced by Production I. G in 1998, and an anime series produced by Toei Animation, which began broadcasting in Japan in 1999. Additionally, Toei has developed thirteen animated feature films, one OVA and eleven television specials. Several companies have developed various types of merchandising such as a trading card game and numerous video games. The manga series was licensed for an English language release in North America and the United Kingdom by Viz Media and in Australia by Madman Entertainment. The anime series was licensed by 4Kids Entertainment for an English-language release in North America in 2004, before the license was dropped and subsequently acquired by Funimation in 2007.